Abstract: PD72-12
Sources of Funding: None

Introduction

Despite improvements in various forms of radiotherapy for prostate cancer over the past 20 years, secondary malignancies remain a concern, especially amongst younger patients. We analyzed a population-based cancer database to compare the risk of bladder, rectum and colon cancer after definitive treatment of prostate cancer with external beam radiotherapy (EBRT) or brachytherapy (BT) compared to surgery; and assessed its differential impact by age at diagnosis. _x000D_

Methods

We analyzed a cohort of 198,738 men from the SEER database diagnosed with localized prostate cancer between 1993 and 2013. We used Cox regression models and to assess the association between BT and EBRT vs. surgery and the likelihood of developing subsequent bladder, rectum or colon cancer 2 or more years after treatment. For subgroup analyses, we separately analyzed these associations in men who were below and above the age of 65 years using a similar analysis. To help account for multiple comparisons p values < .005 were considered statistically significant._x000D_

Results

The incidence of secondary malignancies was low in all groups (~ 4.3%). All three sites showed a statistically significant (p < 0.0001) increase in the hazard of secondary cancers compared to surgery (colon HR: 1.46, 95%, CL: 1.36 - 1.57; rectum HR: 1.78, 95%, CL: 1.59 - 1.99; bladder HR: 2.19, 95%, CL: 2.05 - 2.34). While exposure to radiation was associated with increased hazards in both younger and older men, consistently higher hazards were seen in the younger cohort. We found that EBRT was associated with a higher risk of cancer at all sites in both younger and older men, but BT was not associated with an increased risk of colon or rectal (Table 1). _x000D_

Conclusions

Incidence of bladder, rectum and colon cancer is significantly increased after treatment of prostate cancer with radiotherapy compared to surgery. Effects are observed regardless of age, and worse in men who are younger and those receiving EBRT. _x000D_

Funding

None