Does the addition of oxaliplatin to preoperative chemoradiation benefit cT4 or fixed cT3 rectal cancer treatment? A subgroup analysis from a prospective study

Abstract Background Whether there is any benefit derived from adding oxaliplatin to fluoropyrimidine-based preoperative chemoradiation is currently unknown in cases of advanced cT3 or cT4 tumours. Our aim was to evaluate this issue by analysing a randomized trial, which compared two schedules of preoperative treatment (chemoradiation vs. 5 × 5 Gy with 3 cycles of consolidation chemotherapy) for cT4 or fixed cT3 rectal cancer. Patients and methods Delivery of oxaliplatin was mandatory to the first part of the study. For the second part, its delivery in both treatment-assigned groups was left to the discretion of the local investigator. We analysed a subgroup of 272 patients (136 in the oxaliplatin group and 136 in the fluorouracil-only group) from institutions that had omitted oxaliplatin in the second part of the study. Results Circumferential resection margin negative (CRM−) status rate was 68% in the oxaliplatin group and 70% in the fluorouracil-only group, p = 0.72. The pathological complete response rate (pCR) was correspondingly 14% vs. 7%, p = 0.10. Following multivariable analysis, when comparing the CRM− status in the oxaliplatin group to the fluorouracil-only group, the odds ratio was 0.79 (95 CI 0.35–1.74), p = 0.54; there being no interaction between concomitant chemoradiation and 5 × 5 Gy with consolidation chemotherapy; p interaction  = 0.073. For pCR, the corresponding results were 0.47 (95 CI 0.19–1.16), p = 0.10, p interaction  = 0.84. Conclusion No benefit was found of adding oxaliplatin in terms of CRM nor pCR rates for either concomitant or sequential settings in preoperative radiochemotherapy for very advanced rectal cancer.