Positive surgical margins contribute to the survival paradox between patients with stage IIB/C (T4N0) and stage IIIA (T1-2N1, T1N2a) colon cancer

Background. The underlying reasons for the survival paradox between stage IIB/C and stage IIIA colon cancer are elusive. We hypothesized that positive margins contribute to this paradox. Methods. We evaluated a cohort of 16,471 patients with stage IIIA and stage IIB/C colon cancer from 709,583 cases diagnosed between 2003-2012 in the National Cancer Data Base. All patients had chemotherapy, and all stage IIB/C patients had >= 12 lymph nodes retrieved. Patients with stage IIIA were subdivided further into those with <12 lymph nodes retrieved and those with >= 12 lymph nodes retrieved. Univariable and multivariable survival analyses were used. Results. The 5-year overall survival rate was 70.8% for stage IIB/C, 81.6 % for stage IIIA with <12 lymph nodes, and 85.6% for stage IIIA with >= 12 lymph nodes (P < .0001). The 5-year overall survival rate was 84.3 % for stage IIIA with no residual tumor, 74.8% for stage IIIA with residual tumor, 73.3 % for stage IIB/C with no residual tumor, and 60.5 % for stage IIB/C with residual tumor (P < .0001). Independent predictors (P < .01) of poor overall survival include stage IIB/C, advanced age, African American ethnicity, community cancer program, uninsured and Medicaid, low education level, high comorbidity index, and positive surgical margins. Conclusion. Positive surgical margins may contribute to the survival paradox between stage HB/C and stage IIIA colon cancer patients.