Signals of inequity in the care pathway: rural lab diagnosis, systemic therapy delays, and RAS mutation differences in metastatic colorectal cancer

Introduction Colorectal cancer (CRC) remains a leading cause of mortality in Canada, with outcomes often influenced by geographic disparities. While biomarker testing for RAS, BRAF, and microsatellite instability (MSI) is now standard for metastatic CRC (mCRC), it is unclear if these diagnostic advances are equitably accessible to rural populations. Methods We conducted a retrospective, population-based cohort study of 818 patients diagnosed with stage IV CRC in Saskatchewan between 2017 and 2022. We evaluated differences based on patient residence (rural vs. urban) and diagnosing laboratory location (rural vs. urban) regarding clinical characteristics, biomarker status, treatment delays, and overall survival. Results Rural patients had higher odds of right-sided tumors (aOR 1.76) and rectal tumors (aOR 1.52) compared to urban residents. Notably, RAS mutations were more frequently identified in rural patients (11.2% vs. 1.6%, p=0.021). While overall survival did not differ significantly by residency (median 250 vs. 270 days, p=0.774), patients diagnosed in rural laboratories experienced significantly longer delays from diagnosis to the initiation of chemotherapy (66.5 vs. 55 days, p=0.011) and a clinically relevant, though not statistically significant, delay in immunotherapy (77.5 vs. 65 days). Multivariable analysis confirmed that older age and poorer performance status were the primary predictors of mortality, rather than geography. Discussion In Saskatchewan, stage IV CRC survival is comparable between rural and urban patients; however, the care pathway is hindered by systemic therapy delays linked to rural diagnostic laboratory locations. While survival rates are currently similar, the delays associated with rural laboratory workups represent an actionable target for improvement.