Patterns of Care and Outcomes of Low-Lying Adenocarcinoma and Squamous Cell Carcinoma of the Rectum.

Abstract

Squamous cell carcinoma (SCC) of the rectum is a unique entity that lacks definitive guidelines regarding prognosis and treatment. This study aimed to analyze patterns of care and survival for SCC and adenocarcinoma (AC) of the rectum. This was a retrospective analysis of patients with stage I-III SCC or AC of the rectum treated from 2004 to 2016 from the National Cancer Database. The treatment groups analyzed were surgery alone (S), chemoradiation followed by surgery (CRT + S), surgery followed by chemoradiation (S + CRT), and definitive chemoradiation (CRT). Patient- and clinical-related factors were compared. Overall survival was assessed with the Kaplan-Meier method and Cox proportional regression models. Of the patients studied, 21,587 (97.1%) were AC and 640 (2.9%) were SCC. Among patients with AC, most (n = 8549, 59.4%) received chemoradiation followed by surgery; those with SCC (n = 305, 66.4%) received definitive chemoradiation. Among patients who received surgery, the majority (69.2%) with AC histology had a low anterior resection while the majority (52.1%) of SCC had an abdominoperineal resection. Five-year overall survival of AC versus SCC in the entire cohort was 61.6% versus 56.1%, respectively (p < 0.001). On multivariable analysis for AC, CRT + S (HR 0.61, p < 0.001), or S + CRT (HR 0.67, p < 0.001) had improved survival compared to S alone while those who had definitive CRT (HR 1.55, p < 0.001) had worse survival. SCC of the rectum tends to be treated like anal cancers with definitive chemoradiation, with similar survival to historical reports of anal cancer. AC of the rectum is most commonly treated under the rectal cancer paradigm.