Effect of adjuvant chemotherapy on recurrence-free survival varies by neo-adjuvant treatment in patients with stage III rectal cancer

Introduction: Adjuvant chemotherapy still is a controversial therapy for rectal cancer patients. The aim of this study was to analyze the effect of adjuvant chemotherapy on recurrence-free survival (RFS) for patients with stage III rectal cancer treated in clinical practice, taking into account which neo-adjuvant treatment patients received. Methods: Patients from regions in the Netherlands diagnosed between 1996 and 2013 with pathological stage III rectal cancer who received short-course radiotherapy, chemoradiation or no neo-adjuvant treatment and who underwent surgery were included. After stratification by neo-adjuvant treatment, 5-year RFS according to adjuvant chemotherapy receipt was calculated using Kaplan-Meier curves. Cox regression was used to discriminate the independent effect of adjuvant chemotherapy on the risk of recurrence/death. Results: The study population consisted of 829 patients, of whom 537 (65%) patients received short-course radiotherapy, 128 (15%) patients received chemoradiation and 164 (20%) patients received no neo-adjuvant treatment. Adjuvant chemotherapy was administered to 152 (18%) patients. Adjuvant chemotherapy was associated with improved 5-year RFS for patients who received short-course radiotherapy (61% vs. 46%, p = 0.005) and for patients. who did not receive any neo-adjuvant treatment (70% vs. 28%, p <0.0001). In multivariable analyses, adjuvant chemotherapy was associated with a reduced risk of recurrence/death for patients treated with short-course radiotherapy (HR 0.65, 95% CI 0.46-0.93) and for patients without neo-adjuvant treatment (BR 0.35, 95% CI 0.18-0.71), but not for patients treated with chemoradiation (HR 1.11, 95% CI 0.51-2.41). Conclusion: Among patients with stage III rectal cancer, the effect of adjuvant chemotherapy on RFS seems to vary by neo-adjuvant treatment.