Objective   To investigate the relation between cyclooxygenase-2 (COX-2), microsatellite stability (MSS) expression and prognosis after oxaliplatin chemotherapy in colorectal cancer.

  Methods   A total of 70 patients with colorectal cancer were selected as study objects, and were performed radical resection of colorectal cancer in our hospital, followed by adjuvant chemotherapy with oxaliplatin. The expression levels of COX-2 and MSS in the tissues of colorectal cancer were observed, and the disease free survival time of patients was recorded.

  Results   Of 70 patients, there were 34 patients with positive expression for COX-2 and MSS (double positive group), 12 patients with positive COX-2 and 11 positive for MSS (single positive group), 13 negative for COX-2 and MSS (double negative group). The proportion of TNM classification in stage Ⅲ was 55.88% in double positive group and 43.40% in the single positive group, which were significantly higher than that in the double negative group (P < 0.00.05). The median time of disease free survival was 14 months (95%CI, 13.22 to 14.78), which was significantly shorter than 24 months (95% CI, 21.53 to 26.47) in the single positive group and 34 months (95% CI, 27.35 to 40.65) in the double negative group(P < 0.00.05). The results of Cox proportional risk regression analysis showed that TNM stage, COX-2 and MSS expressions were influencing factors of prognosis in patients with colorectal cancer after chemotherapy with oxaliplatin (HR=2.354, 1.103 and 1.155, P < 0.00.05).

  Conclusion   The positive expressions of COX-2 and MSS can affect the effect of chemotherapy with oxaliplatin in patients with colorectal cancer, and reduce disease free survival time.