Combination of microsatellite instability and lymphocytic infiltrate as a prognostic indicator for adjuvant therapy in colon cancer.

BACKGROUND Microsatellite instability (MSI) and lymphocytic infiltrate (LI) in colon cancer are associated with less aggressive biological characteristics. Patients with stage II disease who are negative for MSI and LI have been found to have a less favorable prognosis. These patients may be candidates for more aggressive adjuvant therapy. OBJECTIVE To evaluate the outcomes of patients with colon cancer treated with and without adjuvant chemotherapy on the basis of stage, MSI, and LI. DESIGN Prospective evaluation of MSI and LI status with retrospective analysis of chemotherapy regimen. SETTING Community hospital system. PATIENTS A total of 167 patients with colon cancer. INTERVENTION Definitive resection of colorectal cancer with or without chemotherapy. Main Outcome Measure Disease-free survival (DFS) with and without chemotherapy according to combined MSI and LI status. RESULTS Data on MSI and LI status and chemotherapeutic regimens were available for 140 patients. The 5-year DFS was 50% for patients with stage II disease who underwent chemotherapy vs 76% for those who did not (P = .02). In the group negative for MSI and LI, 5-year DFS was 29% for those undergoing chemotherapy and 91% for those who did not (P = .001). CONCLUSIONS Forgoing adjuvant chemotherapy should be considered in patients with stage II colon cancer who are negative for MSI and LI. The MSI and LI status shows promise as a combined prognostic marker and may prove particularly useful in selecting patients with stage II disease for adjunctive therapy.