By: Dan Sperling, MD
According to the American Cancer Society (ACS), “Some cancer treatments such as chemotherapy and radiation therapy may increase a person’s risk of developing a different type of cancer later in life.”[i] The ACS identifies prostate cancer as one of the cancers often treated with beam radiation that can lead to other cancers later on. These “secondary” cancers do not mean that the prostate cancer had spread; on the contrary, a new cancer has begun in a nearby organ (bladder, colon, rectum) because of exposure to radiation. The awareness of this potential is not new. Almost a decade ago, a study out of the University of Minnesota, acknowledging that the connection between prostate radiation and bladder cancer was already known, established that beam radiation for prostate cancer increased the risk of rectal cancer.[ii]
Now, a new report from the University of Michigan, based on clinical records of 441,504 men diagnosed with prostate cancer between 1992 and 2010, reports the calculated risk of developing a second primary cancer (rectal or blader) based on whether or not the men had external beam radiation therapy (EBRT) to treat their prostate cancer.[iii] This is important news for patients. There are different forms of external beam radiation, including conventional EBRT, intensity modulated radiation therapy (IMRT), sterotactice body radiation therapy (SBRT), and proton beam therapy. Brachytherapy, or radioactive seed implants, appears to carry less risk of cancer originating in nearby structures, but there is little long term data on it. All radiation has some “scatter,” but the Michigan study examined only EBRT.
How great is the EBRT risk? According to the University of Michigan Health System’s news service, “The researchers looked at the number of secondary cancers that developed 10 or more years after men were diagnosed with prostate cancer. As a whole, men diagnosed with prostate cancer were at a lower risk of developing a second cancer. But when researchers looked at patients who received external beam radiation therapy, they found these patients were estimated to be 70 percent more likely to be diagnosed with a rectal cancer and 40 percent more likely for bladder cancer than the general public.”[iv]
While the study results should not discourage prostate cancer patients from choosing radiation, especially those who are not candidates for surgery, the authors urge physicians to discuss the side effect risks of all treatment, including EBRT, with their patients. In particular, men whose life expectancy is at least 10 years should be aware of the longer term risk of developing bladder, colon or rectal cancer if they are considering radiation as their treatment. The authors advise that radiation patients be monitored for bladder and rectal cancer, though there is currently no established protocol for how that should be done.
Although this study is sobering, it is wise to keep it in perspective. There is not yet a perfect, risk-free prostate cancer treatment. However, the earlier prostate cancer is found, the more treatment options a patient has, including image-guided targeted ablation treatments that have little to no impact on healthy urinary and sexual function. Such approaches represent a relatively low-risk middle ground between no treatment vs. radical (whole-gland) treatment. In today’s prostate cancer world, many factors go into making a treatment decision. It is essential that each patient have an informed grasp of those factors, and how they affect him as an individual.
[ii] Baxter N, Tepper J, Durham S et al. Increased risk of rectal cancer after prostate radiation: A population-based study. Gastroenterology. 2005 Apr;128(4)819-824
[iii] Davis, E. J., Beebe-Dimmer, J. L., Yee, C. L. and Cooney, K. A. (2014), Risk of second primary tumors in men diagnosed with prostate cancer: A population-based cohort study. Cancer. doi: 10.1002/cncr.28769