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

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 progn...