Comparison of survival outcomes of rectal squamous cell carcinoma with rectal adenocarcinoma.

Abstract

745 Background: Rectal squamous cell carcinoma (RSCC) is a rare disease. It is unclear whether the prognosis or treatment outcomes differ from that of rectal adenocarcinoma (RAC). The objective of this study is to compare the overall survival (OS), cancer specific survival (CSS) and prognostic factors of RSCC to those of rectal adenocarcinoma (RAC) using the Surveillance, Epidemiology, and End Results (SEER) registry. Methods: A total of 42,317 patients diagnosed with RSCC (999) and RAC (41,318) without distant metastasis between 1998 and 2011 were identified from the SEER database. Factors analyzed included histology (RSCC/RAC), age (≤56/>56), gender, race (white/nonwhite), tumor size (<5 cm/≥5 cm), grade (well-moderate/poor-undifferentiated), stage (local/regional), year of diagnosis (1998-2003/2004-2011), with or without surgery, and with or without radiotherapy (RT). OS and CSS were evaluated using the Kaplan-Meier method. Cox proportional hazards regression analysis was performed to examine the prognostic factors for survival. Results: The median follow up is 77 months (M). The entire group had 5 year OS and CSS of 62% and 77% with a median OS of 95 M but did not reach a median CSS. Compared to patients with RAC, patients with RSCC tend to be younger, female, diagnosed more recently, with less advanced stage but higher grade and larger tumor size. For patients with RSCC, 40% underwent surgery and 75% received RT. In contrast, for patients with RAC, 89% underwent surgery and 59% received RT. Patients with RSCC had a higher median OS than those with RAC (105 vs 94 M, Log-rank p <0.05). Cox proportional hazards analysis showed that patients with RAC had worse OS (hazard ratio [HR] 1.4) and CSS (HR 1.6) than patients with RSCC (p<0.05), after adjusting for all prognostic factors. Factors associated with improved OS and CSS in both RSCC and RAC included age ≤56, nonwhite, early stage, well-moderate differentiated, undergoing surgery and receiving RT. Gender is a prognostic factor for OS but not for CSS. Conclusions: Patients with rectal squamous cell carcinoma had a significantly superior OS and CSS than patient with rectal adenocarcinoma. Future studies should seek to explore the optimal management for these two distinct diseases.