Background: Achieving the benefits of precision oncology is dependent on timely and appropriate biomarker testing. 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 colorectal cancer for implementation in SmartLinQ, CancerLinQ’s quality platform. Methods: Working collaboratively with a Technical Expert Panel (TEP), ASCO staff successfully developed an eCQM, BRAF Mutational Analysis Results Received for Patients Treated for Metastatic Colorectal Cancer. CancerLinQ tested the implementation of three versions of the measure's technical specifications against data from 61 organizations and multiple electronic health record (EHR) systems. We analyzed the availability of required data elements in native and curated data, and variability and frequency of BRAF mutation testing documentation. The measure was also tested for validity and reliability among volunteer oncology practices. Results: Implementation efforts revealed that BRAF information is infrequently found in structured data fields and often lacks specificity for the specific variant tested. Ultimately, implementation of the measure in CancerLinQ was infeasible due to a lack of BRAF testing data and variant specificity across its active organizations. Reliability testing among oncology practices uncovered a lack of substantial performance gap with an average measure score of 87.4, 95% CI [86.1, 88.8], making the measure unsuitable for Consensus-Based Entity (CBE) endorsement or use in federal reporting programs. Conclusions: While ASCO’s implementation efforts yielded clear benefits, including identification of future CancerLinQ platform enhancements, gaps in the capture of BRAF testing data and inconsistent documentation of BRAF variants across EHR systems prevented successful implementation of the eCQM at this time. These findings underscore the current difficulty in ascertaining the specificity of key molecular variants in structured EHR data alone without human curation or access to unstructured data, as well as an ongoing need for measure stakeholders to advance eCQM standards necessary for supporting future eCQM deployment.