Background: ASCO received funding from the Gordon & Betty Moore Foundation’s Diagnostic Excellence Initiative to develop and test a biomarker electronic Clinical Quality Measure (eCQM) in ovarian cancer. Methods: Working collaboratively with a Technical Expert Panel (TEP), ASCO staff explored the development of an eCQM, Appropriate Germline Testing for Ovarian Cancer Patients to assess the rates of testing for BRCA1/2 germline mutations in adult ovarian cancer patients. The measure underwent clinical workflow analysis; feasibility; face, empiric, and data element validity; and signal-to-noise reliability testing. Results: Feasibility testing indicated an inability to reliably differentiate between germline and somatic BRCA1/2 testing in an eCQM specification due to both a lack of specificity in existing codes, and inconsistent use of appropriate codes to reflect germline testing. Among the 32 individual clinicians across 12 testing sites, overall measure performance ranged from 6.25 to 100 percent, with a 52.3 percent mean performance score (95 percent CI [39.9, 64.7]), indicating a performance gap and variation in care in germline testing among the ovarian cancer patient population. Conclusions: This measure development effort illustrated a scenario where medical practice has advanced beyond current data availability and coding specificity in a way that impacts stakeholder ability to reliably assess the delivery of personalized cancer care and minimize the burden of that measurement. While we concluded the implementation of an eCQM to assess rates of germline testing in ovarian cancer patients was infeasible and premature, ASCO continues to advance the registry-based Clinical Quality Measure (CQM) version of the measure, as testing indicated the CQM is reliable, valid, and reflected continued variation in care. ASCO supports efforts to advance towards robust, meaningful digital quality measures using things like Fast Healthcare Interoperability Resources (FHIR) and Minimal Common Data Elements (mCODE) initiatives, which will enable more standardized data capture and increase the availability and utility of granular data needed for assessing quality cancer care. ASCO also seeks to expand the denominator of this measure to include additional cancer types where germline BRCA1/2 testing is appropriate. Denominator expansion will not only significantly broaden the impact of the measure, but also increase longevity of the measure’s potential use in cross-cutting reporting initiatives such as the Merit-based Incentive Payment System (MIPS) Value Pathways (MVPs).