Background: Neoadjuvant chemoradiotherapy is regarded as the standard of treatment for locally advanced lower rectal cancer although some of these cases are systemic, and local control may be inadequate. We aimed to stratify patients into prognostic groups based on preoperative factors, including response to neoadjuvant chemotherapy. Methods: We retrospectively analyzed patients with locally advanced lower rectal adenocarcinoma (clinical stage II/III with high-risk features of distant metastasis) who were treated with neoadjuvant chemotherapy followed by curative resection between 2010 and 2017 and those, who did not receive neoadjuvant chemoradiotherapy. Reduction in tumor volume (before vs. after neoadjuvant chemotherapy) was measured using magnetic resonance imaging. Recurrence and overall survival were also evaluated.Results: The cohort was composed of 105 patients. Good response to neoadjuvant chemotherapy was associated with better 5-year recurrence-free survival (good responders: 83.3%, poor responders: 50.9%; p=0.001) and 5-year overall survival (good responders: 95.8%, poor responders: 82.5%; p=0.04). In a multivariate analysis, extramural venous invasion on magnetic resonance imaging before neoadjuvant chemotherapy was significantly and independently associated with worse recurrence-free survival (hazard ratio: 2.57, 95% confidence interval: 1.32–5.03, p=0.006). Good responders without extramural venous invasion had the best 5-year recurrence-free and overall survival (89.7% and 94.9%, respectively). Poor responders with extramural venous invasion had the worst 5-year recurrence-free and overall survival (26.7% and 60.0%, respectively).Conclusions: Reductions in tumor volume after neoadjuvant chemotherapy were associated with better prognosis in patients with locally advanced lower rectal cancer. Extramural venous invasion was a preoperative prognostic factor.

Background: Neoadjuvant chemoradiotherapy is regarded as the standard of treatment for locally advanced lower rectal cancer, although some of these cases are systemic, and distant control may be inadequate. Neoadjuvant chemotherapy could compensate for such shortcomings, potentially yielding better survival outcomes. We aimed to stratify patients into prognostic groups on the basis of preoperative factors, including response to neoadjuvant chemotherapy. Methods: We retrospectively analyzed patients with locally advanced lower rectal adenocarcinoma (clinical stage II/III with high-risk features of distant metastasis) who were treated with neoadjuvant chemotherapy (without radiotherapy) followed by curative resection between 2010 and 2017. Reduction in tumor volume (before vs. after neoadjuvant chemotherapy) was measured using magnetic resonance imaging, and a reduction above 60% was defined as a good response. Recurrence and overall survival were evaluated. Results: The cohort comprised 102 patients. Good response to neoadjuvant chemotherapy was associated with better 5-year recurrence-free survival (good responders: 81.1%, poor responders: 49.0%; p =0.001) and 5-year overall survival (good responders: 94.9%, poor responders: 80.6%; p =0.06). In a multivariate analysis, extramural venous invasion on magnetic resonance imaging after neoadjuvant chemotherapy and a tumor volume reduction rate <60 were found to be significantly and independently associated with worse recurrence-free survival (hazard ratio: 2.74, 95% confidence interval: 1.36–5.50, p =0.005 and hazard ratio: 3.48, 95% confidence interval: 1.57–7.72, p =0.002, respectively). Good responders without extramural venous invasion had the best 5-year recurrence-free and overall survival (89.0% and 93.8%, respectively). Poor responders with extramural venous invasion had the worst 5-year recurrence-free and overall survival (21.4% and 50.0%, respectively). Conclusions: Reductions in tumor volume after neoadjuvant chemotherapy were associated with a better prognosis in patients with locally advanced lower rectal cancer. Extramural venous invasion was a preoperative prognostic factor.