ABSTRACT
Objective: To evaluated the prognostic effect of tumor volume in patients with locally advanced rectal cancer (LARC) treated with neoadjuvant chemoradiotherapy (NCRT) and total mesorectal excision (TME). Methods: This was a retrospective analysis of 128 patients with newly diagnosed rectal cancer who received preoperative concurrent chemoradiation plus TME from January 2011 to September 2016 in Hunan Cancer Hospital. The receiver-operating characteristic (ROC) curve was used to analyze the gross tumor volume (GTV) cut-off point. Prognostic analysis was performed using Kaplan-Meier, Log-rank, and Cox regression models. Results: After NCRT, T-stage declined 58.6%, N-stage declined 69.5%, and the overall TNM stage declined 77.3%. After NCRT, the pathological complete response (pCR) rate was 16.4% and the anus-protection rate was 57.03%. The GTV cut-off point was 79.31 mL. There were significant differences in OS, DFS, LRFS and DMFS between patients with GTV ≥79.31 mL and patients with GTV <79.31 mL over three years. GTV was significantly related to MRI-T staging (ρ=0.236; P=0.007), T downstaging (ρ=0.229; P=0.009),TNM downstaging (ρ=0.219; P=0.013), and tumor regression grade (TRG) (ρ=0.517; P<0.001); however, GTV was not significantly related to MRI-N staging and N downstaging. Conclusions: GTV is closely related to local recurrence and distant metastasis of LARC, and is an important prognostic factor. Tumor volume was significantly related to pretreatment MRI-T staging, T downstaging, TNM downstaging after NCRT, and TRG, but not to pretreatment MRI-N staging and N downstaging.