Secondary Bladder Cancers Following Low-Dose Brachytherapy for Prostate Cancer - Expert Commentary
The retrospective study consisted of data from patients who had prostate cancer and bladder cancer. Among these, 51 were included in the prostate brachytherapy cohort and represented the radiation group (study cohort). Researchers for the non-radiation group identified patients with secondary bladder cancer and prostate cancer managed without radiation from the Surveillance, Epidemiology, and End Results (SEER) database. Overall, the two groups had no significant difference in age or median follow-up. However, those in the study cohort developed bladder cancer after a median of 9.5 years after prostate brachytherapy, while those in the SEER cohort developed bladder cancer after a median of 6.3 years after being diagnosed with prostate cancer. Patients who had undergone brachytherapy exhibited tumors involving the bladder neck (19.1%) or trigone (17%). Among the SEER cohort patients, 9.1% of post-prostate cancer tumors exhibited bladder-neck involvement, while 15.2% exhibited trigone involvement. In addition, more patients exhibited high-grade disease in the study cohort (78.4%) compared to the SEER cohort (52.3%), P = 0.0009). Study cohort patients also had a higher proportion of muscle-invasive bladder cancer (MIBC) than SEER patients (35.3% versus 17.5%, respectively). A significantly higher proportion of post-brachytherapy MIBC patients in the study cohort (77.8%) underwent radical cystectomy than MIBC patients in the SEER cohort (32.7%).
Overall the survival and cancer-specific survival rates were similar in both cohorts. However, for patients with MIBC, those in the study cohort had a significantly higher 5-year overall survival rate than MIBC patients in the SEER cohort. In the study cohort, 22 of 51 post-brachytherapy bladder cancer patients exhibited progression during follow-up (median time of 10.5 months). Among these, 10 developed local progression, while 12 patients developed distant metastasis. The overall 5-year progression-free survival among this cohort was 43.7%. Furthermore, recurrence occurred in 62.7% of patients in this cohort, a higher proportion of whom had non-muscle invasive bladder cancer (NMIBC). The median time between the last treatment for bladder cancer and the detection of recurrence was 8.5 months.
The bladder is a common site for secondary cancers after brachytherapy for prostate cancer. This study suggested that these post-radiation bladder cancers are associated with high-grade disease and are more likely to be muscle invasive. Nevertheless, these patients had better survival outcomes than patients in the SEER cohort who did not undergo radiation, which may be due to the higher probability of being treated with cystectomy among the former. However, it should be noted that researchers did not have complete information on treatment details, such as radiation dose for prostate cancer, which can affect outcomes among patients. Another study limitation is that patients in the two cohorts were only matched by age due to limited information on patient characteristics in the SEER database.
Written by: Bishoy M. Faltas, MD, Director of Bladder Cancer Research, Englander Institute for Precision Medicine, Weill Cornell Medicine
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