Adjuvant Radiation Survival Benefits in Patients with Stage 1B Rectal Cancer: A Population-based Study from the Surveillance Epidemiology and End Result Database (1973-2010).

Introduction Rectal cancer remains a leading cause of cancer morbidity and mortality in the United States. Currently, total mesorectal excision (TME) is the standard therapy for patients with T2N0 (stage IB) rectal cancer. Whether adjuvant radiation therapy provides a survival benefit to these patients or exposes them to unnecessary toxicity remains controversial and unproven to date. This study examined a large cohort of Stage 1B rectal cancer patients who underwent surgical resection and received adjuvant radiation in order to determine the demographic, clinical, and pathologic factors impacting prognosis and survival. Methods Demographic and clinical data on 4,054 Stage 1B rectal cancer patients were abstracted from the Surveillance Epidemiology and End Result (SEER) database (1973-2010). Statistical analysis was performed with SPSS v20.0 software (IBM Corp., Armonk, NY) using the chi-square test, paired t-test, multivariate analysis, and Kaplan-Meier functions. Results Among 4,054 patients with stage IB rectal cancer, 2,364 (58.3%) had surgery only, 1,477 (36.4%) received combination surgery and radiation (CSR), 139 (3.4%) received radiation only, and 74 (1.8%) received no therapy. Most stage IB patients in the surgery only and CSR groups were male (65.8 and 64%) and Caucasian (78.2% and 74.2%), p<0.001. Patients receiving CSR were younger than those undergoing surgery alone (63 vs. 69 years, p<0.001). More tumors in the CSR group were 2-4 cm (53.6%), followed by > 4 cm (24%), while fewer were <cm (22.4%). Histologically, most of the tumors in the CSR group were moderately differentiated (83.5%) and adenocarcinoma NOS (95.5%), followed by poorly (9.3%) and mucinous adenocarcinoma (4.5%), well-differentiated (6.8%), and undifferentiated (0.4%). Overall survival was prolonged in the CSR group compared to the surgery-only group (5.85 years vs. 5.44 years, p<0.001), although cancer-specific survival did not differ (6.33 years vs. 6.42 years, p=0.143). Multivariate analysis identified age>60 (OR 2.4), poorly differentiated (OR 1.7) or undifferentiated grade (OR 2.6), and tumor size >2 cm (OR 1.5) as independently associated with increased mortality in the CSR group (p<0.05) while female gender conferred a survival advantage (OR 0.8), p<0.01. Conclusions In the current cohort, CSR was utilized most often in young male Caucasian patients presenting with less advanced disease as compared to other treatment groups. The overall survival is prolonged and overall mortality is lower in patients receiving CSR; however, increased cancer-related mortality with the use of CSR implies that survival benefits may be attributable to favorable non-tumor-related factors such as age, gender, and race. CSR should not replace surgery alone as the standard of care for all Stage IB rectal cancer patients at this time. However, all T2N0 rectal cancer patients should be enrolled in randomized control trials to allow for more defined multimodality management to optimize clinical outcomes for these patients.