BACKGROUNDIt remains controversial whether patients with Stage II colorectal cancer would benefit from adjuvant chemotherapy after radical resection. The aim of this study was to establish two mathematical models to identify the suitable patients for adjuvant chemotherapy.

METHODSThe current study comprised of two steps. In the first step, 353 patients with Stage II colorectal cancer who underwent surgical procedures at the Third Affiliated Hospital of Sun Yat-sen University between June 2006 and December 2015 were entered and followed up for 6-120 months. Their clinical data were collected and enrolled into the database. We established two mathematical models by univariate and multivariate Cox regression analysis to identify the target patients; in the second step, 230 patients under the same standard between January 2012 and December 2016 were entered and followed up for 3-62 months to verify the two models' validation.

RESULTSIn the first step, totally 340 surgical patients with Stage II colorectal cancer were finally enrolled in this study. Statistical analysis showed that tumor differentiation (TD) (P < 0.001), lymphovascular invasion (LVI) (P < 0.001), uncertain or positive margins (UPM) (P < 0.001), and fewer lymph nodes (LNs) (<12) retrieved (P < 0.001) were correlated with the overall survival (OS) and disease free survival (DFS). We obtained two models: (1) OS risk score = 1.116 × TD + 2.202 × LVI + 3.676 × UPM + 1.438 × LN - 0.493; (2) DFS risk score = 0.789 × TD + 2.074 × LVI + 3.183 × UPM + 1.329 × LN - 0.432. According to the models and cutoff points [(0.07, 1.33) and (-0.04, 1.30), respectively], patients can be divided into three groups: low-risk, moderate-risk, and high-risk. Moreover, the high-risk group patients could benefit from adjuvant chemotherapy. In the second step, totally 221 patients were finally used to verify the models' validation. The results proved that the models were accurate and feasible (P< 0.05).

CONCLUSIONSAccording to the predictive models, patients with Stage II colorectal cancer in the high-risk group are strongly recommended for adjuvant chemotherapy, thus facilitating the individualized and precise treatment.