e19042 Background: Several factors affect how medical oncologists in the Philippines, a lower middle income country, incorporate biomarkers in real-world practice. This study described patterns of use of biomarker testing for the management of breast, colorectal, and lung cancers among medical oncologists in the Philippines, where treatment is largely out-of-pocket. Methods: A cross-sectional survey was performed among practicing medical oncologists in the Philippines from November to December 2019. Responses were compiled and summarized using descriptive statistics. Results: A total of 127 responses (about 40% of medical oncologists in the country) were collected. Respondents were both consultants and fellows-in-training who, on the average, had been in oncology practice for 6.64 years (SD 7.37). Majority of respondents were affiliated with private hospitals and/or clinics (62.20%), but 40.94% of medical oncologists worked in academic medical centers. If clinically indicated and if cost did not play a role, 96% of respondents would order ER, PR and HER2neu testing for breast cancer. A quarter of respondents would include Ki-67 testing. In actual practice, 97% of the respondents reported ordering for ER/PR and 93% for HER2neu testing. For lung cancer, respondents would use EGFR (97.76%), PD-L1 (88.19%), ALK (80.31%), ROS1 (58.27%), and BRAF (33.07%). In actual practice, EGFR was the most frequently ordered biomarker (67.72%). 44.80% of medical oncologists had never used ROS1. For colorectal cancer, the respondents would use KRAS (98.43%), NRAS (81.89%), MMR/MSI (82.25%), and BRAF (63.78%), but these were only sometimes used. 59.84% of medical oncologists had never used BRAF. The strongest factor that drove medical oncologists to test for biomarkers was adherence to clinical practice guidelines (96%), with most respondents using international guidelines from the United States and Europe (61.4%). The largest barrier to biomarker use in the Philippines was financial constraints (94.5%), followed by the patients’ unwillingness to be tested (59.1%), and unavailability of tests in the areas of practice (58.27%). Conclusions: Medical oncologists in the Philippines would use biomarkers in the management of breast, colorectal, and lung cancers if these were clinically indicated and if cost did not play a role. Biomarker use was largely driven by American and European clinical practice guidelines. Financial difficulties by patients, who often had to resort to out-of-pocket payments for their treatment, formed the largest barrier to biomarker use.