Prostate cancer radiotherapy raises bladder, rectal cancer risk

September 1, 2008

Men who receive some form of radiotherapy for localized prostate cancer have an elevated risk of later developing bladder and rectal cancers.

A retrospective study of 243,082 men treated between 1988 and 2003 showed that those who had undergone external beam radiation therapy, brachytherapy, or a combination of the two had a statistically significant increased risk of developing a bladder tumor compared with those who had undergone radical prostatectomy.

The risk of rectal cancer also was elevated in radiation-treated men, although it was not as high as bladder cancer risk and was notable mainly in men who had received external beam radiation.

"Urologists should be alert for hematuria in patients with a history of radiation for prostate cancer," said Dr. Soloway, professor and chairman of urology at the University of Miami. "Hematuria can easily be attributed to radiation cystitis, but bladder cancer is a sufficiently common cause that a more extensive workup to include cystoscopy and urinary cytology should be considered."

Patient data were culled from the Surveillance, Epidemiology, and End Results database. Almost half of the patients (45%) had undergone radical prostatectomy, while another 39% had received external beam therapy, 9% had received brachytherapy, and 7% had received a combination of the two forms of radiation.

Multivariate analysis showed that the relative risk of developing bladder cancer was 1.88 after external beam, 1.52 after brachytherapy, and 1.85 after combination therapy, compared with prostatectomy. There were no differences in the stage or grade of bladder tumors by treatment received.

The odds of developing post-treatment rectal cancer were 1.26 for external beam, 1.08 for brachytherapy, and 1.21 for the two together, compared with radical prostatectomy. The elevated risk for both cancers persisted at 10-year follow-up.

"We should note that the absolute risk of developing either of these cancers remains low," said study co-author Alan M. Nieder, MD, assistant professor of urology, University of Miami. "But these data do further demonstrate the biologic basis for some sort of effect from radiation treatment."

Compared with the general U.S. population, the standardized incidence ratio for developing bladder cancer following radical prostatectomy was only 0.99, compared with 1.42 for external beam radiation, 1.10 for brachytherapy, and 1.39 for the combination approach. Similarly, the numbers for rectal cancer were 0.91, 0.99, 0.68, and 0.86, respectively.

Dr. Nieder said urologists should be aware that there may be a subset of patients for whom prostatectomy is a better option than radiation, such as heavy smokers, who are already at increased risk of bladder cancer.

"Despite advances in radiation therapy technology, the number of these cases of post-radiation bladder and rectal tumors appears to be increasing," said Dr. Soloway. "That should give [urologists] pause as they follow patients treated for localized prostate cancer."