OBJECTIVES: Biomarker testing is recommended in guidelines at metastatic colorectal cancer (mCRC) diagnosis; yet real-world testing patterns are not fully known. This research aims to investigate real-world biomarker testing (KRAS, NRAS, BRAF, and Microsatellite Instability (MSI)) in mCRC patients and to understand patient and practice characteristics associated with testing.

METHODS: A retrospective analysis of patients diagnosed with mCRC between 2013–Q2 2020 was performed using data from the Flatiron Health mCRC database. Patients were included if they were ≥18 years old, had ≥2 visits in the Flatiron Network, and had ≥2 months of continuous follow-up from the date of metastatic diagnosis. Exclusion criteria included no activity within 90 days after mCRC diagnosis date or death date prior to mCRC diagnosis date.

RESULTS: 25,861 patients met eligibility criteria. Testing rates increased between 2013 and 2019 for all biomarkers except KRAS (18.9% to 63.6% for NRAS; 27.5% to 67.6% for BRAF; and 33.5% to 83.9% for MSI); testing rates for KRAS remained stable (71.1% to 74.2%). In 2018 – 2019, a significant trend of lower testing rates with increasing age or lower testing in patients who had higher (2+) ECOG performance (PS) at diagnosis was observed. Testing did not appear to vary across sex, race, or stage at initial diagnosis. Most tests occurred at or prior to first treatment regimen (MSI: 93.2%; KRAS: 90.1%; NRAS: 90.1%; BRAF: 89.5%). Median time from mCRC diagnosis to first biomarker test ranged from 0.7 – 1.3 months. Mean time ranged from 1.7 – 2.8 months. From 2013 – 2020, 9,504 patients were tested for all four biomarkers.

CONCLUSIONS: Biomarker testing rates increased over time, possibly in response to guideline recommendations. Testing rates are similar across sex and race. A gap of ~20-40% in biomarker testing remains versus the guideline recommended rate of 100% mCRC patients tested.