Predictive factors associated with relapse of stage II/III colon cancer treated with peroral anti-cancer agents in the adjuvant setting.

Postoperative adjuvant chemotherapy for patients with stage III colon cancer (CC) is regarded as the standard treatment worldwide for outcome improvement and relapse prevention. Similarly, high-risk stage II CC requires adjuvant chemotherapy because of its high recurrence rate. Previous randomized controlled trials showed that oxaliplatin (OX), in addition to fluorinated pyrimidine-based therapy for patients with stage II/III CC, significantly improves cancer survival but it remains controversial as to which patient groups should receive OX-containing regimens. Among 1,150 consecutive patients who underwent curative resection for stage II/III CC between 2009 and 2016 at two tertiary hospitals, 349 patients treated with only peroral (PO) fluorinated pyrimidine-based chemotherapy and 149 patients who received fluorinated pyrimidine-based chemotherapy with OX as adjuvant chemotherapy were retrospectively reviewed. The primary outcome was recurrence-free survival (RFS). Clinicopathological factors were more advanced in patients treated with OX than in patients treated only with PO fluorinated pyrimidine agents. Multivariate analysis for 5-year RFS showed that T4 [hazard ratio (HR), 2.947; P=0.0001], N2 (HR, 2.704; P=0.0075), vessel or lymphatic invasion (HR, 1.675; P=0.0437) and high cancer antigen (CA)19-9 (HR 3.367, P=0.0002) levels were independent risk factors of cancer relapse. Propensity score matching analysis was performed to match clinicopathological differences between the PO and OX groups. After matching, subgroup analysis of the patients showed that greater effects of OX on cancer survival were observed in patients in the OX group with high CA19-9 levels and tended to be associated with T4 and N2 compared with the PO group. Thus, OX-containing regimens should be recommended for patients with CC with these factors in an adjuvant setting.