Abstract 4204: Racial difference in the risk of secondary bladder cancer following radiation therapy among prostate cancer patients
Authors: Zhang Lu , Hsieh Mei-Chin , Yu Qingzhao , Wu Xiao-Cheng 
Published: August 2019

Abstract
Purpose: Radiation therapy has been found associated with increased risk of secondary bladder cancer diagnosis among prostate cancer patients. It is unknown whether this association varies by race. This study aimed to investigate whether the association between radiation and secondary bladder cancer differs for white vs. black prostate cancer patients.
Methods: Data on white or black men who were diagnosed with primary localized prostate cancer in Louisiana between 2004 and 2013 and received radiation only or surgery only were obtained from Louisiana Tumor Registry. We excluded those who developed secondary bladder cancer within 180 days of the prostate cancer diagnosis or had follow-up less than 180 days or with unknown tumor size or Gleason score. Every patient was followed up until the end of 2016. The exposure variable was treatment (radiation only vs. surgery only). The outcome variable was the diagnosis of secondary bladder cancer and the time from prostate cancer diagnosis to secondary bladder cancer diagnosis or to loss to or end of follow-up. Covariates included age at diagnosis, marital status, insurance, census tract level poverty, tumor size, and Gleason score group. The competing risk survival analysis was applied. Death during follow-up was considered as competing event. Analysis was stratified by race.
Results: Of 10,861 white and 5,117 black prostate cancer patients, 52.7% and 56.8% received only radiation respectively. Regardless of race, patients who only received surgery were younger, more likely to be married, privately insured, live in low poverty census tract, and have smaller or lower grade tumor (P &lt;0.0001 for each in both racial groups). Among white prostate cancer patients who received surgery only vs. radiation only, 31 (0.60%) vs. 127 (2.22%) of them developed secondary bladder cancer (P &lt; 0.0001). Among black surgery only vs. radiation only patients, 14 (0.63%) vs. 29 (1.00%) of them developed a secondary bladder cancer (P = 0.16). The median follow-up time was 8.9, 8.0, 8.3, and 7.6 years for white surgery, white radiation, black surgery, and black radiation patients, respectively. After adjusting for covariates, the hazard ratio (95% confidence interval) [HR (95% CI)] of developing secondary bladder cancer was 2.70 (1.58, 4.61) for white radiation patients compared to white surgery patients; 0.95 (0.31, 2.89) for black radiation patients compared to black surgery patients. Compared to white surgery patients, the HR (95% CI) of developing secondary bladder cancer was 1.16 (0.61, 2.22) and 1.38 (0.74, 2.56) for black surgery and black radiation patients, respectively.
Conclusions: Radiation is associated with increased risk of secondary bladder cancer among white prostate cancer patients, but not among black patients. Early screening of secondary bladder cancer need to be emphasized among white prostate cancer patients who received radiation therapy.
Citation Format: Lu Zhang, Mei-Chin Hsieh, Qingzhao Yu, Xiao-Cheng Wu. Racial difference in the risk of secondary bladder cancer following radiation therapy among prostate cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4204.