Effect of Adjuvant Chemotherapy on Stage II Rectal Cancer Outcomes After Preoperative Short-Course Radiotherapy

Background: Adjuvant chemotherapy (AC) is offered to patients with stage II rectal cancer, but its use is controversial. We examined population-based outcomes of patients with pathologic stage II rectal cancer treated with AC after preoperative short-course radiotherapy.

Materials and methods: We included patients diagnosed with pathologic stage II tumors from 1999 to 2009 in British Columbia. The disease-specific survival (DSS), relapse-free (RFS), and overall survival (OS) were assessed. Multivariate models adjusting for age, gender, Eastern Cooperative Oncology Group, and high-risk features (ie, pT4, poor differentiation, < 12 lymph nodes removed, lymphovascular invasion, perineural invasion, or obstruction or perforation) were constructed.

Results: Of 851 patients reviewed, 330 had received preoperative short-course radiotherapy, of whom 123 (37%) subsequently received AC. Patients treated with AC were younger (median age 61 vs. 73 years; P < .0001), reported better Eastern Cooperative Oncology Group status (P < .0001), and had more high-risk features (P < .0001). On univariate analysis, AC was associated with improved DSS (hazard ratio [HR], 0.58; 95% confidence interval [CI], 0.36-0.94; P = .028), RFS (HR, 0.62; 95% CI, 0.39-0.98; P = .043), and OS (HR, 0.42; 95% CI, 0.30-0.59; P < .0001). On multivariate analysis, these outcomes were not significant (DSS HR, 0.83; 95% CI, 0.43-1.61; P = .58; RFS HR, 0.82; 95% CI, 0.44-1.50; P = .51; OS HR, 0.62; 95% CI, 0.37-1.03; P = .064). Subgroup analysis suggested AC improved DSS (HR, 0.25; 95% CI, 0.07-0.89; P = .033), RFS (HR, 0.24; 95% CI, 0.07-0.85; P = .027), and OS (HR, 0.22; 95% CI, 0.069-0.70; P = .011) only in patients with ≥ 2-high risk features.

Conclusion: In the present population-based cohort of patients with stage II rectal cancer, AC did not improve the outcomes in unselected patients. In a small subgroup of patients with ≥ 2 risk factors, we noted improved outcomes with AC use.