EBRT patients may be at higher risk for later mortality

Patients who undergo external beam radiation therapy (EBRT) either as primary treatment for prostate cancer or for post-prostatectomy positive margins are at increased risk of mortality if they later develop bladder or colorectal secondary malignancies, researchers from the University of California Davis in Sacramento reported here.

In addition, the researchers said that when patients with locally advanced or metastatic disease were excluded, only those who later specifically developed bladder and colorectal cancers were significantly negatively affected in terms of overall and secondary malignancy-specific survival.

Patients who received radiation were almost twice as likely to develop a secondary malignancy compared with those who were not exposed (odds ratio, 1.89; 95% confidence interval, 1.85-1.95).

The risk of developing secondary tumors following EBRT has been previously addressed by a variety of investigators, said first author Karim Chamie, MD, who worked on the study with Ralph deVere White, MD, and colleagues.

"The argument as to whether there is an increased risk of bladder and colorectal cancers among those treated with EBRT is primarily one of statistical analysis - simple odds ratio versus Cox proportional-type hazard models," Dr. Chamie said.

The UC Davis group, however, took the analysis to the next level, examining disease-specific survival after radiation treatment. Dr. Chamie and his team found that secondary malignancy-specific survival was significantly worse for patients treated with EBRT who developed bladder or colorectal cancers.

Conversely, radiotherapy for prostate cancer was not associated with worse secondary malignancy-specific survival in men who developed renal, respiratory, hematologic, small intestine, or hepatobiliary cancers.

Data for the study were culled from the Surveillance, Epidemiology, and End Results (SEER) database of the National Cancer Institute. The cohort included 130,375 prostate cancer patients treated with EBRT and 375,235 who did not receive radiation. Exclusion criteria included brachytherapy, unknown radiotherapy, previous malignancy, and development of a new malignancy within 1 year of initial prostate cancer diagnosis.