Although reported absolute rates of second malignancies after radiotherapy for prostate cancer are very low, it is associated with higher rates of bladder, colon, and rectal cancers in patients who undergo radiotherapy for prostate cancer. This systematic review and meta-analysis compared patients exposed to radiotherapy with patients unexposed.1
The researchers emphasized that, while risk was increased, the absolute rates of these secondary cancers remain low, particularly compared with the rates of other complications associated with treatment for prostate cancer, including urinary incontinence and erectile dysfunction.
In this study, the results of 21 studies that assessed the risk of secondary malignancies in patients with prostate cancer who were and were not exposed to radiotherapy were analyzed.
The meta-analysis found an increased risk of cancers of the bladder, colorectum, and rectum, but not lung or hematologic cancers, after radiotherapy compared with no radiotherapy or surgery. These findings were consistent whether the analyses were restricted to studies using 5-year or 10-year lag periods between treatment and the development of a secondary cancer.
The absolute risks for developing a secondary cancer associated with undergoing radiotherapy for prostate cancer were 0.1% to 3.8% for bladder cancer, 0.3% to 4.2% for colorectal cancer, and 0.3% to 1.2% for rectal cancers.
The researchers suggest that these findings could be used in discussing treatment options with patients, particularly those patients with a life expectancy of 20 years or more.
“This information could be particularly important to a large proportion of patients where treatment is recommended and according to treatment guidelines where surgery or radiation would be equal options for them to choose,” said corresponding author Robert K. Nam, MD, of the Sunnybrook Research Institute at the University of Toronto, Ontario, Canada.
This study “confirms our belief that second malignancy should be added to the already long list of avoidable hazards associated with treatment for those men with low risk prostate cancer who simply need no treatment at all,” stated an accompanying editorial, written by 2 US experts based at Harvard Radiation Oncology Program and Massachusetts General Hospital in Boston.2
The editorial concluded that concern about second malignancies “should not, however, stand in the way of an effective and well-studied treatment being given to men with higher grade, lethal prostate cancer for whom the potential benefit simply dwarfs the risk.”
1. Wallis CJ, Mahar AL, Choo R, et al. Second malignancies after radiotherapy for prostate cancer: systematic review and meta-analysis. BMJ. 2016;352:i851.
2. Eyler EC, Zietman AL. A (relatively) risky business: the link between prostatic radiotherapy and second malignancies. BMJ. 2016;352:i1073.