Combination of primary tumor location and mismatch repair status guides adjuvant chemotherapy in stage II colon cancer.

Background: Current opinions on the benefits of adjuvant chemotherapy for stage II colon cancer are divided and reformative election of these patients is required. We examined whether the primary tumor location based on mismatch repair status and other risk factors could better inform the current guideline.

Materials and Methods: A total of 673 consecutive patients with stage II colon cancer were included in the analysis. Differences in the common clinicopathological factors between left-sided colon cancer and right-sided colon cancer were analyzed using Fisher's exact analysis. Kaplan-Meier analysis was used to distinguish the survival difference by primary tumor location and/or MMR status.

Results: RCC had a shorter overall survival ( P = 0.001) and Disease-free survival ( P = 0.050) than LCC but was associated with survival benefit from adjuvant chemotherapy ( P = 0.001 and P = 0.011 for OS and DFS, respectively). Mismatch repair-proficient had a shorter OS ( P = 0.036) and disease free survival ( P = 0.034) than mismatch-repair deficient but chemotherapy improved the OS ( P = 0.007). When the primary tumor location and MMR status were combined, the PMMR/RCC was the only subgroup that could benefit from adjuvant chemotherapy ( P < 0.001 and P = 0.002 for OS and DFS, respectively). Other tumors such as DMMR/RCC, DMMR/LCC, and PMMR/LCC did not benefit.

Conclusions: The observed survival benefits in PMMR/RCC patients treated with adjuvant chemotherapy will allow better selection of patients for chemotherapy who are in stage II.