<?xml version="1.0" encoding="us-ascii"?>
<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2021-10-28T14:12:16.6749053+00:00 -->
<!-- Version            : 5.0.1.702 -->
<!-- Package ID         : c47755444a54496e9b610537436907b6 -->
<!-- Copyright (c) 2021 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
<xsd:schema xmlns:dei="http://xbrl.sec.gov/dei/2021" xmlns:us-types="http://fasb.org/us-types/2021-01-31" xmlns:stpr="http://xbrl.sec.gov/stpr/2021" xmlns:srt-types="http://fasb.org/srt-types/2021-01-31" xmlns:exch="http://xbrl.sec.gov/exch/2021" xmlns:sic="http://xbrl.sec.gov/sic/2021" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:srt="http://fasb.org/srt/2021-01-31" xmlns:enum2="http://xbrl.org/2020/extensible-enumerations-2.0" xmlns:us-gaap="http://fasb.org/us-gaap/2021-01-31" xmlns:naics="http://xbrl.sec.gov/naics/2021" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:country="http://xbrl.sec.gov/country/2021" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:currency="http://xbrl.sec.gov/currency/2021" xmlns:fulc="http://www.fulcrumtx.com/20210930" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2020-01-21" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.fulcrumtx.com/20210930" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:import schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" namespace="http://www.xbrl.org/2003/instance" />
  <xsd:import schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" namespace="http://www.xbrl.org/2003/linkbase" />
  <xsd:import schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" namespace="http://xbrl.org/2005/xbrldt" />
  <xsd:import schemaLocation="https://www.xbrl.org/2020/extensible-enumerations-2.0.xsd" namespace="http://xbrl.org/2020/extensible-enumerations-2.0" />
  <xsd:import schemaLocation="https://xbrl.sec.gov/country/2021/country-2021.xsd" namespace="http://xbrl.sec.gov/country/2021" />
  <xsd:import schemaLocation="https://xbrl.sec.gov/currency/2021/currency-2021.xsd" namespace="http://xbrl.sec.gov/currency/2021" />
  <xsd:import schemaLocation="https://xbrl.sec.gov/dei/2021/dei-2021.xsd" namespace="http://xbrl.sec.gov/dei/2021" />
  <xsd:import schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd" namespace="http://www.xbrl.org/dtr/type/2020-01-21" />
  <xsd:import schemaLocation="https://xbrl.sec.gov/exch/2021/exch-2021.xsd" namespace="http://xbrl.sec.gov/exch/2021" />
  <xsd:import schemaLocation="http://www.xbrl.org/lrr/arcrole/factExplanatory-2009-12-16.xsd" namespace="http://www.xbrl.org/2009/arcrole/fact-explanatoryFact" />
  <xsd:import schemaLocation="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd" namespace="http://www.xbrl.org/2009/role/negated" />
  <xsd:import schemaLocation="http://www.xbrl.org/lrr/role/net-2009-12-16.xsd" namespace="http://www.xbrl.org/2009/role/net" />
  <xsd:import schemaLocation="https://xbrl.sec.gov/naics/2021/naics-2021.xsd" namespace="http://xbrl.sec.gov/naics/2021" />
  <xsd:import schemaLocation="https://xbrl.sec.gov/sic/2021/sic-2021.xsd" namespace="http://xbrl.sec.gov/sic/2021" />
  <xsd:import schemaLocation="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd" namespace="http://fasb.org/srt/2021-01-31" />
  <xsd:import schemaLocation="https://xbrl.fasb.org/srt/2021/elts/srt-roles-2021-01-31.xsd" namespace="http://fasb.org/srt-roles/2021-01-31" />
  <xsd:import schemaLocation="https://xbrl.fasb.org/srt/2021/elts/srt-types-2021-01-31.xsd" namespace="http://fasb.org/srt-types/2021-01-31" />
  <xsd:import schemaLocation="https://xbrl.sec.gov/stpr/2021/stpr-2021.xsd" namespace="http://xbrl.sec.gov/stpr/2021" />
  <xsd:import schemaLocation="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd" namespace="http://fasb.org/us-gaap/2021-01-31" />
  <xsd:import schemaLocation="https://xbrl.fasb.org/us-gaap/2021/elts/us-roles-2021-01-31.xsd" namespace="http://fasb.org/us-roles/2021-01-31" />
  <xsd:import schemaLocation="https://xbrl.fasb.org/us-gaap/2021/elts/us-types-2021-01-31.xsd" namespace="http://fasb.org/us-types/2021-01-31" />
  <xsd:annotation>
    <xsd:appinfo>
      <link:roleType id="TemplateLink" roleURI="http://www.fulcrumtx.com/20210930/role/TemplateLink" xmlns:link="http://www.xbrl.org/2003/linkbase">
        <link:definition>00000 - Document - Template Link</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="fulc-20210930_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:title="Calculation Links, all" xlink:type="simple" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="fulc-20210930_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:title="Definition Links, all" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="fulc-20210930_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:title="Label Links, all" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="fulc-20210930_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:title="Presentation Links, all" xlink:type="simple" />
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DocumentDocumentAndEntityInformation" id="Role_DocumentDocumentAndEntityInformation">
        <link:definition>100000 - Document - Document and Entity Information</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/StatementConsolidatedBalanceSheetsUnaudited" id="Role_StatementConsolidatedBalanceSheetsUnaudited">
        <link:definition>100010 - Statement - Consolidated Balance Sheets (Unaudited)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/StatementConsolidatedBalanceSheetsUnauditedParenthetical" id="Role_StatementConsolidatedBalanceSheetsUnauditedParenthetical">
        <link:definition>100020 - Statement - Consolidated Balance Sheets (Unaudited) (Parenthetical)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/StatementConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited" id="Role_StatementConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited">
        <link:definition>100030 - Statement - Consolidated Statements of Operations and Comprehensive Loss (Unaudited)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/StatementConsolidatedStatementsOfStockholdersEquityUnaudited" id="Role_StatementConsolidatedStatementsOfStockholdersEquityUnaudited">
        <link:definition>100040 - Statement - Consolidated Statements of Stockholders&apos; Equity (Unaudited)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/StatementConsolidatedStatementsOfCashFlowsUnaudited" id="Role_StatementConsolidatedStatementsOfCashFlowsUnaudited">
        <link:definition>100050 - Statement - Consolidated Statements of Cash Flows (Unaudited)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureNatureOfBusinessAndBasisOfPresentation" id="Role_DisclosureNatureOfBusinessAndBasisOfPresentation">
        <link:definition>100060 - Disclosure - Nature of the Business and Basis of Presentation</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies" id="Role_DisclosureSummaryOfSignificantAccountingPolicies">
        <link:definition>100070 - Disclosure - Summary of Significant Accounting Policies</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureFairValueMeasurements" id="Role_DisclosureFairValueMeasurements">
        <link:definition>100080 - Disclosure - Fair Value Measurements</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCashEquivalentsAndMarketableSecurities" id="Role_DisclosureCashEquivalentsAndMarketableSecurities">
        <link:definition>100090 - Disclosure - Cash Equivalents And Marketable Securities</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosurePropertyAndEquipmentNet" id="Role_DisclosurePropertyAndEquipmentNet">
        <link:definition>100100 - Disclosure - Property and Equipment, Net</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureAdditionalBalanceSheetDetail" id="Role_DisclosureAdditionalBalanceSheetDetail">
        <link:definition>100110 - Disclosure - Additional Balance Sheet Detail</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosurePreferredStock" id="Role_DisclosurePreferredStock">
        <link:definition>100120 - Disclosure - Preferred Stock</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCommonStock" id="Role_DisclosureCommonStock">
        <link:definition>100130 - Disclosure - Common Stock</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureStockBasedCompensationExpense" id="Role_DisclosureStockBasedCompensationExpense">
        <link:definition>100140 - Disclosure - Stock-based Compensation Expense</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCollaborationAndLicenseAgreements" id="Role_DisclosureCollaborationAndLicenseAgreements">
        <link:definition>100150 - Disclosure - Collaboration and License Agreements</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureRightOfReferenceAndLicenseAgreement" id="Role_DisclosureRightOfReferenceAndLicenseAgreement">
        <link:definition>100160 - Disclosure - Right of Reference and License Agreement</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingencies" id="Role_DisclosureCommitmentsAndContingencies">
        <link:definition>100170 - Disclosure - Commitments and Contingencies</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureDefinedContributionPlan" id="Role_DisclosureDefinedContributionPlan">
        <link:definition>100180 - Disclosure - Defined Contribution Plan</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureNetLossPerShare" id="Role_DisclosureNetLossPerShare">
        <link:definition>100190 - Disclosure - Net Loss per Share</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies" id="Role_DisclosureSummaryOfSignificantAccountingPoliciesPolicies">
        <link:definition>100200 - Disclosure - Summary of Significant Accounting Policies (Policies)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureFairValueMeasurementsTables" id="Role_DisclosureFairValueMeasurementsTables">
        <link:definition>100210 - Disclosure - Fair Value Measurements (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCashEquivalentsAndMarketableSecuritiesTables" id="Role_DisclosureCashEquivalentsAndMarketableSecuritiesTables">
        <link:definition>100220 - Disclosure - Cash Equivalents And Marketable Securities (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosurePropertyAndEquipmentNetTables" id="Role_DisclosurePropertyAndEquipmentNetTables">
        <link:definition>100230 - Disclosure - Property and Equipment, Net (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureAdditionalBalanceSheetDetailTables" id="Role_DisclosureAdditionalBalanceSheetDetailTables">
        <link:definition>100240 - Disclosure - Additional Balance Sheet Detail (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCommonStockTables" id="Role_DisclosureCommonStockTables">
        <link:definition>100250 - Disclosure - Common Stock (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureStockBasedCompensationExpenseTables" id="Role_DisclosureStockBasedCompensationExpenseTables">
        <link:definition>100260 - Disclosure - Stock-based Compensation Expense (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingenciesTables" id="Role_DisclosureCommitmentsAndContingenciesTables">
        <link:definition>100270 - Disclosure - Commitments and Contingencies (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureNetLossPerShareTables" id="Role_DisclosureNetLossPerShareTables">
        <link:definition>100280 - Disclosure - Net Loss per Share (Tables)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureNatureOfBusinessAndBasisOfPresentationAdditionalInformationDetails" id="Role_DisclosureNatureOfBusinessAndBasisOfPresentationAdditionalInformationDetails">
        <link:definition>100290 - Disclosure - Nature of the Business and Basis of Presentation - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureFairValueMeasurementsFinancialAssetsMeasuredAtFairValueOnRecurringBasisAndLevelOfFairValueHierarchyClassificationDetails" id="Role_DisclosureFairValueMeasurementsFinancialAssetsMeasuredAtFairValueOnRecurringBasisAndLevelOfFairValueHierarchyClassificationDetails">
        <link:definition>100300 - Disclosure - Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis and Level of Fair Value Hierarchy Classification (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformationDetails" id="Role_DisclosureFairValueMeasurementsAdditionalInformationDetails">
        <link:definition>100310 - Disclosure - Fair Value Measurements - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCashEquivalentsAndMarketableSecuritiesSummaryOfMarketableSecuritiesDetails" id="Role_DisclosureCashEquivalentsAndMarketableSecuritiesSummaryOfMarketableSecuritiesDetails">
        <link:definition>100320 - Disclosure - Cash Equivalents And Marketable Securities - Summary of Marketable Securities (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCashEquivalentsAndMarketableSecuritiesAdditionalInformationDetails" id="Role_DisclosureCashEquivalentsAndMarketableSecuritiesAdditionalInformationDetails">
        <link:definition>100330 - Disclosure - Cash Equivalents And Marketable Securities - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosurePropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNetDetails" id="Role_DisclosurePropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNetDetails">
        <link:definition>100340 - Disclosure - Property and Equipment, Net - Schedule of Property and Equipment, Net (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosurePropertyAndEquipmentNetAdditionalInformationDetails" id="Role_DisclosurePropertyAndEquipmentNetAdditionalInformationDetails">
        <link:definition>100350 - Disclosure - Property and Equipment, Net - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureAdditionalBalanceSheetDetailScheduleOfPrepaidExpensesAndOtherCurrentAssetsDetails" id="Role_DisclosureAdditionalBalanceSheetDetailScheduleOfPrepaidExpensesAndOtherCurrentAssetsDetails">
        <link:definition>100360 - Disclosure - Additional Balance Sheet Detail - Schedule of Prepaid Expenses and Other Current Assets (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureAdditionalBalanceSheetDetailScheduleOfAccruedExpensesAndOtherCurrentLiabilitiesDetails" id="Role_DisclosureAdditionalBalanceSheetDetailScheduleOfAccruedExpensesAndOtherCurrentLiabilitiesDetails">
        <link:definition>100370 - Disclosure - Additional Balance Sheet Detail - Schedule of Accrued Expenses and Other Current Liabilities (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosurePreferredStockAdditionalInformationDetails" id="Role_DisclosurePreferredStockAdditionalInformationDetails">
        <link:definition>100380 - Disclosure - Preferred Stock - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCommonStockAdditionalInformationDetails" id="Role_DisclosureCommonStockAdditionalInformationDetails">
        <link:definition>100390 - Disclosure - Common Stock - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCommonStockScheduleOfPotentialConversionOfPreferredStockAndFutureIssuanceOfCommonStockDetails" id="Role_DisclosureCommonStockScheduleOfPotentialConversionOfPreferredStockAndFutureIssuanceOfCommonStockDetails">
        <link:definition>100400 - Disclosure - Common Stock - Schedule of Potential Conversion of Preferred Stock and Future Issuance of Common Stock (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureStockBasedCompensationExpenseAdditionalInformationDetails" id="Role_DisclosureStockBasedCompensationExpenseAdditionalInformationDetails">
        <link:definition>100410 - Disclosure - Stock-based Compensation Expense - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureStockBasedCompensationExpenseSummaryOfRestrictedStockActivityUnder2019PlanAnd2016PlanDetails" id="Role_DisclosureStockBasedCompensationExpenseSummaryOfRestrictedStockActivityUnder2019PlanAnd2016PlanDetails">
        <link:definition>100420 - Disclosure - Stock-based Compensation Expense - Summary of Restricted Stock Activity under 2019 Plan and 2016 Plan (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureStockBasedCompensationExpenseSummaryOfStockOptionActivityDetails" id="Role_DisclosureStockBasedCompensationExpenseSummaryOfStockOptionActivityDetails">
        <link:definition>100430 - Disclosure - Stock-based Compensation Expense - Summary of Stock Option Activity (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureStockBasedCompensationExpenseSummaryOfWeightedAverageAssumptionsUsedToCalculateFairValueOfStockOptionDetails" id="Role_DisclosureStockBasedCompensationExpenseSummaryOfWeightedAverageAssumptionsUsedToCalculateFairValueOfStockOptionDetails">
        <link:definition>100440 - Disclosure - Stock-based Compensation Expense - Summary of Weighted Average Assumptions Used to Calculate Fair Value of Stock Option (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureStockBasedCompensationExpenseSummaryOfRestrictedStockActivityOutsideOf2019And2016PlanDetails" id="Role_DisclosureStockBasedCompensationExpenseSummaryOfRestrictedStockActivityOutsideOf2019And2016PlanDetails">
        <link:definition>100450 - Disclosure - Stock-based Compensation Expense - Summary of Restricted Stock Activity outside of 2019 and 2016 Plan (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureStockBasedCompensationExpenseSummaryOfStockBasedCompensationExpenseRecognizedDetails" id="Role_DisclosureStockBasedCompensationExpenseSummaryOfStockBasedCompensationExpenseRecognizedDetails">
        <link:definition>100460 - Disclosure - Stock-based Compensation Expense - Summary of Stock-Based Compensation Expense Recognized (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCollaborationAndLicenseAgreementsAdditionalInformationDetails" id="Role_DisclosureCollaborationAndLicenseAgreementsAdditionalInformationDetails">
        <link:definition>100470 - Disclosure - Collaboration and License Agreements - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureRightOfReferenceAndLicenseAgreementAdditionalInformationDetails" id="Role_DisclosureRightOfReferenceAndLicenseAgreementAdditionalInformationDetails">
        <link:definition>100480 - Disclosure - Right of Reference and License Agreement - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetails" id="Role_DisclosureCommitmentsAndContingenciesAdditionalInformationDetails">
        <link:definition>100490 - Disclosure - Commitments and Contingencies - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfFutureMinimumLeasePaymentsDetails" id="Role_DisclosureCommitmentsAndContingenciesScheduleOfFutureMinimumLeasePaymentsDetails">
        <link:definition>100500 - Disclosure - Commitments and Contingencies - Schedule of Future Minimum Lease Payments (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureDefinedContributionPlanAdditionalInformationDetails" id="Role_DisclosureDefinedContributionPlanAdditionalInformationDetails">
        <link:definition>100510 - Disclosure - Defined Contribution Plan - Additional Information (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.fulcrumtx.com/20210930/taxonomy/role/DisclosureNetLossPerShareScheduleOfAntidilutiveSecuritiesExcludedFromCalculationOfDilutedNetLossPerShareAttributableToCommonStockholdersDetails" id="Role_DisclosureNetLossPerShareScheduleOfAntidilutiveSecuritiesExcludedFromCalculationOfDilutedNetLossPerShareAttributableToCommonStockholdersDetails">
        <link:definition>100520 - Disclosure - Net Loss per Share - Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders (Details)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xsd:appinfo>
  </xsd:annotation>
  <xsd:element id="fulc_CashAndCashEquivalentsAccumulatedGrossUnrealizedGainsBeforeTax" name="CashAndCashEquivalentsAccumulatedGrossUnrealizedGainsBeforeTax" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_CashAndCashEquivalentsAccumulatedGrossUnrealizedLossesBeforeTax" name="CashAndCashEquivalentsAccumulatedGrossUnrealizedLossesBeforeTax" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_CashEquivalentsAndMarketableSecuritiesAccumulatedGrossUnrealizedGainsBeforeTax" name="CashEquivalentsAndMarketableSecuritiesAccumulatedGrossUnrealizedGainsBeforeTax" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_CashEquivalentsAndMarketableSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" name="CashEquivalentsAndMarketableSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_CashEquivalentsAndMarketableSecuritiesFairValueDisclosure" name="CashEquivalentsAndMarketableSecuritiesFairValueDisclosure" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_AccruedLiabilitiesAndOtherCurrentLiabilities" name="AccruedLiabilitiesAndOtherCurrentLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_LeaseIncentivePayableNoncurrent" name="LeaseIncentivePayableNoncurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues" name="TemporaryEquityStockIssuedDuringPeriodSharesNewIssues" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_IncreaseDecreaseInDeferredRentAndDeferredLeaseIncentive" name="IncreaseDecreaseInDeferredRentAndDeferredLeaseIncentive" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_ProceedsFromMaturityOfMarketableSecurities" name="ProceedsFromMaturityOfMarketableSecurities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_NetProceedsFromIssuancesOfCommonStockInPublicOfferings" name="NetProceedsFromIssuancesOfCommonStockInPublicOfferings" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_PublicOfferingCostsUnpaid" name="PublicOfferingCostsUnpaid" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_RightOfReferenceAndLicenseAgreementDisclosureTextBlock" name="RightOfReferenceAndLicenseAgreementDisclosureTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_OffBalanceSheetRiskAndConcentrationsOfCreditRiskPolicyPolicyTextBlock" name="OffBalanceSheetRiskAndConcentrationsOfCreditRiskPolicyPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_ScheduleOfPrepaidExpensesAndOtherCurrentAssetsTableTextBlock" name="ScheduleOfPrepaidExpensesAndOtherCurrentAssetsTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_ScheduleOfAccruedExpensesAndOtherCurrentLiabilitiesTableTextBlock" name="ScheduleOfAccruedExpensesAndOtherCurrentLiabilitiesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_TwoThousandNineteenAndTwoThousandSixteenStockIncentivePlanMember" name="TwoThousandNineteenAndTwoThousandSixteenStockIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_GrantsOutsideOfTwoThousandSixteenStockIncentivePlanAndTwoThousandNineteenStockIncentivePlanMember" name="GrantsOutsideOfTwoThousandSixteenStockIncentivePlanAndTwoThousandNineteenStockIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_NatureOfBusinessAndBasisOfPresentationLineItems" name="NatureOfBusinessAndBasisOfPresentationLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_NatureOfBusinessAndBasisOfPresentationTable" name="NatureOfBusinessAndBasisOfPresentationTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_PiperSandlerCoMember" name="PiperSandlerCoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_AtTheMarketOfferingMember" name="AtTheMarketOfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_PercentageOfCommissionOnGrossSalesPricePerShare" name="PercentageOfCommissionOnGrossSalesPricePerShare" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_CorporateBondsMember" name="CorporateBondsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_FairValueTransfersBetweenLevels" name="FairValueTransfersBetweenLevels" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_CashAndCashEquivalentsAmortizedCost" name="CashAndCashEquivalentsAmortizedCost" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_CashEquivalentsAndMarketableSecuritiesAmortizedCostBasis" name="CashEquivalentsAndMarketableSecuritiesAmortizedCostBasis" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_ProceedsFromSaleOfMarketableSecurities" name="ProceedsFromSaleOfMarketableSecurities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_LabEquipmentMember" name="LabEquipmentMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_PrepaidExpenses" name="PrepaidExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_PrepaidSignOnBonusesSubjectToVestingProvisions" name="PrepaidSignOnBonusesSubjectToVestingProvisions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_AccruedResearchAndDevelopmentExpenses" name="AccruedResearchAndDevelopmentExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_AccruedRestrictedStockLiabilityCurrent" name="AccruedRestrictedStockLiabilityCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_TemporaryEquityDividendsDeclared" name="TemporaryEquityDividendsDeclared" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_NumberOfCommonStockVotingRights" name="NumberOfCommonStockVotingRights" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="fulc_SharesReservedForConversionOfPreferredStockAndFutureIssuanceOfCommonStock" name="SharesReservedForConversionOfPreferredStockAndFutureIssuanceOfCommonStock" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="fulc_GrantsUnderTwoThousandNineteenStockIncentivePlanMember" name="GrantsUnderTwoThousandNineteenStockIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_GrantsUnderTwoThousandNineteenEmployeeStockPurchasePlanMember" name="GrantsUnderTwoThousandNineteenEmployeeStockPurchasePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_TwoThousandSixteenStockIncentivePlanMember" name="TwoThousandSixteenStockIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_TwoThousandNineteenStockIncentivePlanMember" name="TwoThousandNineteenStockIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_IncreaseInCommonStockCapitalSharesReservedForFutureIssuance" name="IncreaseInCommonStockCapitalSharesReservedForFutureIssuance" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_IncreaseInNumberOfSharesReservedForIssuancePercentOfCommonStockOutstanding" name="IncreaseInNumberOfSharesReservedForIssuancePercentOfCommonStockOutstanding" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsRepurchasedInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsRepurchasedInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsRepurchasedInPeriodWeightedAverageGrantDateFairValue" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsRepurchasedInPeriodWeightedAverageGrantDateFairValue" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_ResearchDevelopmentAndSalesArrangementAggregateAmountReceivableUponAchievementOfMilestone" name="ResearchDevelopmentAndSalesArrangementAggregateAmountReceivableUponAchievementOfMilestone" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_RangeOfTieredRoyaltiesOnNetSales" name="RangeOfTieredRoyaltiesOnNetSales" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="fulc_NonRefundableUpfrontPaymentsReceived" name="NonRefundableUpfrontPaymentsReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_ResearchMilestoneMember" name="ResearchMilestoneMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_ClinicalAndRegulatoryMilestonesMember" name="ClinicalAndRegulatoryMilestonesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_WorldwideNetSalesMilestonesMember" name="WorldwideNetSalesMilestonesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_MyoKardiaCollaborationAgreementMember" name="MyoKardiaCollaborationAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_ChangeInVariableConsiderationConstrained" name="ChangeInVariableConsiderationConstrained" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_ResearchDevelopmentAndSalesArrangementAmountReceivedUponAchievementOfMilestone" name="ResearchDevelopmentAndSalesArrangementAmountReceivedUponAchievementOfMilestone" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_UnbilledAccountsReceivableRelatedToReimbursableResearchAndDevelopmentCost" name="UnbilledAccountsReceivableRelatedToReimbursableResearchAndDevelopmentCost" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_DeferredRevenueCurrentAndNoncurrent" name="DeferredRevenueCurrentAndNoncurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_ReimbursementPaymentRecieved" name="ReimbursementPaymentRecieved" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_UpfrontPayment" name="UpfrontPayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_PaymentForPrepaidResearchFunding" name="PaymentForPrepaidResearchFunding" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_MilestonePaymentForCertainIdentifiedTargets" name="MilestonePaymentForCertainIdentifiedTargets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_MilestonePaymentForCertainOtherIdentifiedTargets" name="MilestonePaymentForCertainOtherIdentifiedTargets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_PrepaidResearchFundingPaymentReceived" name="PrepaidResearchFundingPaymentReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_ClinicalAndRegulatoryMilestonePayables" name="ClinicalAndRegulatoryMilestonePayables" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="fulc_ClinicalAndRegulatoryMilestonePayablesUponPhaseTwoClinicalTrial" name="ClinicalAndRegulatoryMilestonePayablesUponPhaseTwoClinicalTrial" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_SalesMilestone" name="SalesMilestone" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_SeriesBConvertiblePreferredStockMember" name="SeriesBConvertiblePreferredStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_GSKAgreementMember" name="GSKAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_AreaOfPropertiesHeldUnderOperatingLeases" name="AreaOfPropertiesHeldUnderOperatingLeases" type="dtr-types:areaItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="fulc_CommitmentsAndContingenciesLineItems" name="CommitmentsAndContingenciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_CommitmentsAndContingenciesTable" name="CommitmentsAndContingenciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_CommitmentForOfficeAndLaboratorySpaceLeaseOfCurrentCorporateHeadquartersMember" name="CommitmentForOfficeAndLaboratorySpaceLeaseOfCurrentCorporateHeadquartersMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_LegalProceedingsMember" name="LegalProceedingsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="fulc_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFour" name="LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFour" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="fulc_DefinedContributionPlanName" name="DefinedContributionPlanName" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
</xsd:schema>
