Patients with prostate cancer considering radiation therapy should now be informed that radiotherapy raises the risk of developing a secondary cancer. Prostate cancer patients who undergo radiotherapy raise their risk of getting other cancers by nearly 70 percent, according to the results of a new study.

There is a well-documented association between exposure to radiation and carcinogenesis. Previous studies have shown that radiotherapy causes new cancers in patients treated for Hodgkin’s lymphoma. It has however been more difficult to spot a link in prostate cancer because men develop it when they are much older and do not live long enough for a secondary cancer to develop.

Researchers in the US and Canada recently evaluated 21 clinical studies to determine if treatment with radiation increased the risk of developing a new cancer. Their analysis was reported in the British Medical Journal this week and suggests that the risk of developing bowel cancer within 10 years of radiotherapy increased 68 percent; rectal cancer increased by 62 percent; and bladder cancer by 39 percent.

Overall the research suggests that up to one extra person in 200 will develop bladder cancer because of radiotherapy over a 10 year period, and around one in 100 for bowel and rectal cancer.

Although the overall chance of developing cancer following radiation is still quite low, radiotherapy may be an avoidable risk for many men undergoing treatment for prostate cancer.

Radiation therapy is typically used for men with lower risk prostate cancer and surgery is equally effective. Therefore the risk of radiation is completely avoidable because surgery offers an effective alternative treatment. Radiation will remain an important treatment option for many men with prostate cancer but may now be less attractive particularly for younger individuals with lower risk disease that have a very long life expectancy.

The risk of developing a second malignancy should be added to the list of potential complications associated with radiation treatment of prostate cancer and appropriately factored into decision making between patients and their treating physician.

Reference: Wallis C, Mahar A, Choo R, et al. Second malignancies after radiotherapy for prostate cancer: systematic review and meta-analysis. Britsh Medical Journal. 2016;352:i851.

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