LAUSR

533 Background: Approximately 12-15% of all CRCs are associated with defects in the DNA MMR pathway. NCCN 2017 guidelines endorsed universal MMR/MSI testing for all pts with a personal history of CRC. The study objective was to assess US physicians’ MMR/MSI genetic testing practices for mCRC pts. Methods: A non-interventional, cross-sectional online survey was conducted among 151 physicians (91 oncologists, 15 surgeons and 45 pathologists) treating mCRC pts in the US. A draft survey was first developed based on a targeted literature review and exploratory interviews with 15 physicians, and then pilot tested with a new series of 10 physicians. Physicians were eligible if they were US based with at least 5 years of experience treating CRC pts, had at least one mCRC pt in their routine care in the past 6 months of practice, and experienced with MMR/MSI testing including having ordered at least 1 MMR/MSI test for CRC in the past 6 months. Physicians were invited to participate through a market research panel. Descriptive and logistic regression analyses were performed. Results: Awareness of specific MMR/MSI testing guidelines was high (N = 127, 84.1%). Of those, 93.7% (119/127) physicians had awareness of specific published guidelines with majority 67.2% (80/119) being aware of NCCN guidelines. Universal testing for all CRC pts was performed by 68.9% (104/151) physicians, while 29.8% (45/151) selectively orders the test for some CRC pts. Key barriers for testing included insufficient tissue sample to enable running the test (48.3%, 73/151), patient refusal to have the test done (35.8%, 54/151) and insurance cost concerns for the pts (31.1%, 47/151), while 27.2% (41/151) reported no barriers. There were no statistically significant differences based on physician specialty, practice type and years of practice. Conclusions: The survey demonstrated high awareness and compliance with MMR/MSI testing guidelines although universal testing rates seem to be suboptimal. Addressing the key physician barriers to testing along with increased communication and education on the benefits of testing may help to enhance testing rates.