Risk of secondary urinary bladder cancer (UBC) in patients receiving radiotherapy for rectal cancer, prostate cancer, and gynecologic malignancies.

Abstract

363 Background: Radiotherapy proximal to the bladder mucosa may incite malignant transformation. We investigated this phenomenon using a large population-based national database. Methods: The SEER13 database from 1992 to 2012 was reviewed for bladder cancer patients who had a history of any previous cancer, including solid tumors and hematologic malignancies. Data regarding the use of radiotherapy was reviewed. Information was analyzed using standardized incidence ratios (SIRs), defined as the ratio of observed to expected cases adjusted by person years at risk. SIRs are considered statistically significant if corresponding 99% exact confidence intervals (CIs) exclude 1.0. All results were standardized using a referent population matched to the index cases based on age, sex, race, and time period. Results: A total of 20,341 patients with secondary UBC were identified. A higher incidence in secondary UBC was seen amongst rectal, prostate cervical and uterine cancer patients receiving radiotherapy (see Table). Patients with lung cancer had a higher incidence of secondary UBC irrespective of radiotherapy use. Compared to patients with secondary UBC and no prior radiotherapy, patients with secondary UBC with prior radiotherapy had a higher rate of localized disease (79% vs 75%, P < 0.0001) and had poorer survival on multivariate analysis (HR 1.06, 95%CI 1.05-1.06; P < 0.0001). Conclusions: Patients with selected abdominal and pelvic tumors who received radiotherapy had a higher rate of secondary UBC. Further study is needed to determine whether these cancers represent a biologically distinct entity. [Table: see text]