Radiation Therapy Improves Survival in Small Cell Rectal Cancer: Analysis of Surveillance, Epidemiology, and End Results (SEER) Data

Abstract

Purpose/Objective(s): Small cell rectal cancer is a rare entity with scant literature to guide treatment. We used SEER data to investigate the role of radiation therapy (RT) in the management of this unusual cancer. Materials/Methods: The SEER database (National Cancer Institute) was queried using software for cases of small cell rectal cancer. Locoregional cases were defined using the “SEER Historic Stage A” variable to exclude patients with distant metastatic disease. Years of diagnosis were limited to 1988-2009 to reduce variability in staging criteria or longitudinal changes in surgery and radiation techniques. Two month conditional survival was applied to minimize bias by excluding patients who did not survive long enough to receive cancer-directed therapy. Overall survival was compared between patients who received RT (RT) and those who did not (No_RT) using the Kaplan-Meier method. Multivariate Cox proportional hazards model was used to evaluate important covariates, with AJCC Stage as a stratification variable. Case data were extracted and analyzed. Results: A total of 70 cases of locoregional small cell rectal cancer met the study criteria, No_RT Z 29 and RT Z 41. There were 23 deaths in each group. Median survival was significantly longer for patients who received radiation (RT 30 months vs No_RT 9 months, log-rank p Z 0.003). This corresponded to a higher 2-year overall survival rate for those who received radiation (56.8% vs 23.2%). Unadjusted hazard ratio for death (HR) was 0.43 with the use of radiation (95% CI, 0.24-0.76). Cox proportional hazards model (see Table) identified radiation therapy as the only significant factor for overall survival, multivariate HR Z 0.30 (95% CI, 0.150.62; p Z 0.001). Age, surgery and sex were not significant covariates. Conclusions: Small cell rectal cancer is a rare disease with no proven standard of care. Using the SEER data, we have identified a significant survival advantage with the use of radiation therapy. No survival benefit was seen with surgical resection, although this study lacked power to exclude small to moderate differences. Known limitations of the SEER data apply to this study, especially the lack of information on chemotherapy usage. Our findings strongly support the use of radiation therapy for patients with locoregional small cell rectal cancer. Author Disclosure: H.C. Hsu: None. C.G. Leichman: None. K.L. Du: None.