Tumor pathological response and downstaging of locally advanced rectal cancer after neoadjuvant chemoradiotherapy: comparison of two radiation dose schedules

Objective: To assess the short-term efficacy and tolerability of different radiotherapy doses schedules as 46 Gy and 50 Gy for locally advanced rectal cancer patients undergoing neoadjuvant chemoradiotherapy. Methods: All patients with locally advanced rectal cancer who had received neoadjuvant chemoradiotherapy between Aug 2010 and May 2015 were enrolled. This retrospective analysis was performed according to the radiotherapy dose grouping of 46 Gy and 50 Gy groups. Concurrent chemotherapy regimen was capecitabine-based and oxaliplatin was added only when young patients (< 75 years old) were in a good condition. Total mesorector excision was scheduled 6-8 weeks after concurrent chemoradiotherapy. Results: Totally 213 patients were enrolled in our analysis, including 61 cases in 46 Gy group and 152 cases in 50 Gy group. There were 145 male and 68 female patients. There were 22 patients diagnosed clinically with T₂, 180 with T₃, and 11 with T₄. Tumor distance from the anal verge was ≤ 5, > 5 and < 10 cm, or ≥ 10 cm in 82, 115 and 16 patients, respectively. T downstaging was observed in 95 (44.6%) patients, pathologic complete response (PCR) was shown in 48 (22.5%) patients. In the 46 Gy and 50 Gy groups, the rate of PCR was 18.0% vs.24.3% (P > 0.05). In addition, good response rate (TRG 3 + 4) was 67.2% vs. 75.0% (P > 0.05), and T downstaging rate was 39.3% vs. 46.7% (P > 0.05). Subgroup analysis for T₃N₂/T₄ patients, the rate of PCR was 6.3% vs. 23.3% (P > 0.05), good response rate (TRG 3 + 4) was 50.0% vs. 72.1% (P > 0.05), and T downstaging was 31.3% vs. 46.5% (P > 0.05). There was no significant difference in treatment-related toxicity between the two groups. Conclusions: The two different radiation dose fractionation (50 Gy vs. 46 Gy) had no impact on pathologic tumor regression and T downstaging for locally advanced rectal cancer. Nonetheless, a further long-term follow-up is warranted to confirm the preliminary study. (authors)