Adjuvant chemotherapy is not associated with improved survival for all high-risk factors in stage II colon cancer

Adjuvant chemotherapy can be considered in high-risk stage II colon cancer comprising pT4, poor/undifferentiated grade, vascular invasion, emergency surgery and/or <10 evaluated lymph nodes (LNs). Adjuvant chemotherapy administration and its effect on survival was evaluated for each known risk factor. All patients with high-risk stage II colon cancer who underwent resection and were diagnosed in the Netherlands between 2008 and 2012 were included. After stratification by risk factor(s) (vascular invasion could not be included), Cox regression was used to discriminate the independent association of adjuvant chemotherapy with the probability of death. Relative survival was used to estimate disease-specific survival. A total of 4,940 of 10,935 patients with stage II colon cancer were identified as high risk, of whom 790 (16%) patients received adjuvant chemotherapy. Patients with a pT4 received adjuvant chemotherapy more often (37%). Probability of death in pT4 patients receiving chemotherapy was lower compared to non-recipients (3-year overall survival 91% vs. 73%, HR 0.43, 95% CI 0.28-0.66). The relative excess risk (RER) of dying was also lower for pT4 patients receiving chemotherapy compared to non-recipients (3-year relative survival 94% vs. 85%, RER 0.36, 95% CI 0.17-0.74). For patients with only poor/undifferentiated grade, emergency surgery or <10 LNs evaluated, no association between receipt of adjuvant chemotherapy and survival was observed. In high-risk stage II colon cancer, adjuvant chemotherapy was associated with higher survival in pT4 only. To prevent unnecessary chemotherapy-induced toxicity, further refinement of patient subgroups within stage II colon cancer who could benefit from adjuvant chemotherapy seems indicated.