Long-Term Results of a Prospective Phase 2 Study on Volume De-Escalation in Neoadjuvant Chemoradiotherapy of Rectal Cancer.

Purpose: In the current study, we evaluated whether neoadjuvant chemoradiotherapy with reduced treatment volumes due to the exclusion of elective pelvic nodal irradiation is a feasible strategy for selected patients with locally advanced rectal cancer.

Methods And Materials: Patients with T2 low-lying/T3, N0-N1 rectal lesions without evidence of disease in the lateral lymph nodes were prospectively recruited. All patients underwent pretreatment testing, including computed tomography imaging of the chest, abdomen, and pelvis with intravenous contrast, pelvic magnetic resonance imaging with intravenous contrast, and 18-fluorodeoxyglucose positron emission/computed tomography. The clinical target volume included the primary tumor and the mesorectum with vascular supply containing the perirectal and presacral nodes, with the upper border at the S2/S3 interspace. The total radiation dose was 50.4 Gy, and fluoropyrimidine-based chemotherapy was associated concomitantly. The primary endpoint of the study was the reduction of gastrointestinal (GI) toxicity, and the secondary endpoints were pathologic complete response, local control, overall survival, and disease-free survival.

Results: Fifty-two patients (30 men, 22 women) with a median age of 67 years (range, 45-85 years) were enrolled in the study. Acute grade 3 GI toxicity was 7.6%, and there were no cases of grade 4 toxicity. Three patients (5.7%) developed a local recurrence. No relapse occurred in the lateral lymph nodes. The local control rate at 5 years was 96.1%. With a median follow-up time of 72.9 months (range, 2.5-127.6 months), the 3- and 5-year overall survival rates were 89.4% and 87%, respectively. The 3- and 5-year disease-free survival rates were 82.4% and 82.4%, respectively.

Conclusions: De-escalation of radiation therapy target volume reduces GI side effects without compromising efficacy in patients with rectal cancer. These results cannot be clearly extended to high-risk disease and need further evaluation in future randomized trials.