Chemoradiotherapy for squamous cell carcinoma of the rectum: a retrospective propensity-score matched analysis

A lack of evidence-based data on the chemoradiotherapy (CRT) efficacy in patients with squamous cell carcinoma of the rectum (SCCR) makes further study of this topic extremely important.Aim: The aim of our research was to estimate the efficacy of CRT in patients with SCCR compared to the rectal adenocarcinoma and squamous cell carcinoma of the anal canal (SCCAC).Materials and methods: Our study was based on analysis of medical records of patients with ICD-X code C20 and ICD-O 8070 / 3, 8070 / 3.1, 80703 in a database from 2007 to 2020 obtained from the archive of Research Institute FSBI “N. N. Blokhin Cancer Research Center” of the Ministry of Health of Russia. We included patients with SCCR who received CRT as initial treatment into the experimental group. Groups with rectal adenocarcinoma and SCCAC were created using propensity-score matching 1:2 taking into account sex, age, the cN clinical stage, histological grade and tumor size. The main study endpoints were 3-year overall survival (OS) and disease-free survival (DFS) rates, complete clinical response rate and complete clinical or pathological response rate at 6 months after CRT, local recurrence and distant metastases rates, surgery rate.Results: We included 15 patients in SCCR group and 30 patients in rectal adenocarcinoma group and SCCAC group each. There were no significant differences in parameters that could affect the prognosis. The complete clinical response was achieved in 7 (46.7 %) patients with SCCR versus 3 (10.0 %) patients with adenocarcinoma (p = 0.005) and 24 (80.0 %) patients with SCCAC (p = 0.005). The surgery rate was 26.6 % (4 patients) in SCCR group, 6.67 % (2 patients) in SCCAC group, 90 % (27 patients) in adenocarcinoma group (p 0.99). In SCCAC group metastases were detected in 1 (3.3 %) patient, which was significantly different compared to the SCCR group (p = 0.019). Median follow up was 44 months. The 3-year OS was 78.8 % in SCCR group versus 91.0 % in adenocarcinoma group (p = 0.675), and 86.3 % in SCCAC group (p = 0.953). The 3-year OS in adenocarcinoma and SCCAC groups did not differ (p = 0.996). The 3-year DFS was 34.7 % in SCCR group versus 55.6 % in adenocarcinoma group (p = 0.504) and 82.9 % in SCCAC group (p = 0.031). The 3-year DFS differences in adenocarcinoma and SCCAC groups were significant (p = 0.041).Conclusions: We have obtained important data on the CRT comparative efficacy in patients with SCCR, SCCAC and rectal adenocarcinoma. The high complete clinical response rate in SCCR group makes it possible to consider the use of CRT as the main treatment method. Results of our research can be used to plan the treatment of patients with SCCR.