Comparison of prognosis for locally advanced T4b rectal cancer with different pelvic compartment involvement treated using neoadjuvant chemoradiotherapy and implications for refinement of the current TNM staging system

Abstract

Abstract Purpose Although classified as one stage, T4b rectal cancer actually represents a group of heterogeneous diseases. Our study aimed to assess the prognosis of locally advanced T4b rectal cancer involving inferior pelvic and other pelvic compartments. This information may be helpful in further refinement of the current TNM staging system. Methods We retrospectively analysed data from 195 patients with magnetic resonance imaging-identified locally advanced T4b rectal cancer who received neoadjuvant chemoradiotherapy between January 2010 and December 2019. 104 patients had only inferior pelvic compartment involvement (group A) while 91 patients had anterior, posterior or lateral pelvic compartment involvement (group B). Short-term and long-term outcomes were compared between the two groups. Results After neoadjuvant therapy, 80.8% of patients (84/104) in group A and 92.3% of patients (84/91) in group B underwent surgery. The R0 resection rates were 97.6% and 89.3%, respectively (P = 0.061). In addition, 8.7% patients (9/104) in group A achieved clinical complete response and adopted watch-and-wait strategy. Patients in group A had significantly superior 5-year progression-free survival (PFS) (67.8% vs. 55.5%, P = 0.032) and overall survival (OS) (89.6% vs. 71.8%, P = 0.001) than group B. Multivariable Cox regression analysis also identified pelvic compartment involvement classification as an independent predictor of OS (hazard ratio 3.477, P = 0.004). Conclusion T4b rectal cancers with only inferior pelvic compartment involvement had superior prognosis than those involving other pelvic compartments. These differences should be investigated further and taken into consideration in refinement of the TNM staging system.