Efficacy analysis of radiotherapy combined with surgery for locally advanced rectal mucinous adenocarcinoma: a retrospective study based on data of Surveillance, Epidemiology, and End results population

Abstract

To explore the efficacy of radiotherapy combined with surgery for locally advanced rectal mucinous adenocarcinoma. Clinical data of patients with locally advanced rectal mucinous adenocarcinoma (T3-4 and/or N+) diagnosed by postoperative pathology from 1992 to 2013 were retrieved from the US Surveillance, Epidemiology, and End Results (SEER) database. Patients with local excision only, tumor biopsy or combined organ excision and incomplete follow-up information were excluded. All the enrolled patients were divided into three groups according to different treatments, including surgery alone (SA) group, preoperative radiotherapy combined with surgery (RT+S) group and surgery combined with postoperative radiotherapy (S+RT) group. The extracted data included basic data of patients and tumor, treatment status, and follow-up results. The χ² test was used to compare the count data. Kaplan-Meier method was used to draw the survival curve and calculate the survival rate. The survival was analyzed and compared by Log-rank test. The R language 2.8.1 was used to match the patients as 1:1 pairing through the propensity score matching (PSM). The matching variables included gender, age at diagnosis, year at diagnosis, ethnicity, degree of tissue differentiation, TNM stage, depth of invasion, making the baseline data of subgroups comparable. The Cox proportional hazard model was used for multivariate analysis of prognostic factors. A total of 2 149 patients with locally advanced rectal mucinous adenocarcinoma were enrolled in the study, including 1 255 males (58.4%) and 894 females (41.6%). There were 706 patients (32.9%) in the SA group, 772 patients (35.9%) in the RT+S group and 671 patients (31.2%) in the S+RT group. In SA, RT+S and S+RT groups, the median overall survival time was 39, 85, and 74 months respectively; the 5-year overall survival (OS) rate was 38.7%, 56.5%, and 55.2% respectively; the median cancer-specific survival (CSS) time was 86, 127, and 111 months respectively, and the 5-year CSS rate was 53.7%, 62.2% and 60.7% respectively. In comparison among the 3 groups, the 5-year OS rate and CSS rate in the SA group were significantly lower than those in the RT+S group and S+RT group (all P<0.001); the 5-year OS rate and CSS rate between RT+S group and S+RT group were not significantly different (P=0.166 and 0.392,respectively). After the baseline data of subgroups were corrected through PSM, the 5-year OS rate and CSS rate in the SA group (n=375) were significantly lower than those in the RT+S group (n=375)(OS:40.1% vs. 54.5%, P<0.001; CSS:54.3% vs. 63.3%, P=0.023). The 5-year OS rate and CSS rate in the SA group (n=403) were also lower than those in the S+RT group (n=403) (OS:37.4% vs. 54.7%,P<0.001;CSS:51.6% vs. 61.0%,P=0.031). The 5-year OS rate and CSS rate between RT+S group (n=363) and S+RT group (n=363) were not significantly different (OS:51.7% vs. 55.5%, P=0.789; CSS:57.7% vs. 60.5%, P=0.484). Cox multivariate analysis showed that radiotherapy (HR=0.845, 95%CI: 0.790 to 0.903, P=0.001) was an independent prognostic factor for OS of locally advanced rectal mucinous adenocarcinoma; radiotherapy (HR=0.907, 95% CI: 0.835 to 0.985, P=0.021) was also an independent prognostic factor affecting CSS in patients with locally advanced rectal mucinous adenocarcinoma. As compared with surgery alone, surgery combined with preoperative or postoperative radiotherapy is beneficial to the long-term survival of patients with locally advanced rectal mucinous adenocarcinoma.