RT in Prostate Cancer Linked With Low Risk of Secondary Cancers

Men who receive radiation therapy as treatment for their prostate cancer may have an increased risk of developing a subsequent, secondary cancer, according to the results of a meta-analysis of observational studies published in BMJ.

Christopher J. D. Wallis, MD, of the University of Toronto, and colleagues found that radiotherapy for prostate cancer was specifically linked with a higher rate of developing colon, rectal, and bladder cancers. Still, the absolute rates of the secondary cancers among the prostate cancer patients were low.

“It is important to note, however, that the differences in absolute risks between cases and controls were low,” wrote the study authors in their discussion. “In post hoc analysis, the absolute risk difference for patients with radiotherapy compared with those not treated for radiotherapy ranged from −0.9 to 1.9 cancers per 100 patients, with differences observed based on type of radiotherapy, comparator group, and lag time duration indicating that absolute risk for these secondary cancers is low.”

The highest absolute rates of bladder, colorectal, and rectal cancers were 3.8%, 4.2%, and 1.2%, respectively. The lowest reported rates for the same cancers were 0.1%, 0.3%, and 0.3%, respectively.

Odds of a secondary cancer among men treated for their prostate cancer varied by the type of radiation therapy received. “Treatment with external beam radiotherapy was consistently associated with increased odds while brachytherapy was not,” wrote the authors.

The analyses did not restrict the amount of time between radiotherapy and secondary cancer development. The findings were similar when the study authors analyzed the data based on 5- and 10-year time periods following radiotherapy.

The study authors analyzed 21 studies looking at type of radiotherapy used and the risk of bladder, colorectal tract, rectum, lung, and hematologic malignancies. Of the 21 studies, 13 studies used patients who had surgery but no systemic radiotherapy as the control group.

There was no consistent link between radiotherapy for prostate cancer and secondary lung cancer or hematologic malignancies.

The results do not warrant changes to current therapeutic regimen decisions for most men with high-grade prostate cancer, wrote Christine E. Eyler, MD, of the Harvard Radiation Oncology Program, and Anthony L. Zietman, MD, professor of radiation oncology at Massachusetts General Hospital in Boston, in an accompanying editorial.

“From the perspective of the radiation oncologist, this study ‘firms up’ the suspicion that irradiation of the prostate increases the risk of second bladder and colorectal cancers in a time dependent manner. A pragmatist, however, might ask, what are the real world implications for individual patients? Despite an impressive relative risk, the absolute risk remains small, and the cancers discovered, although certainly requiring treatment, might not be lethal,” they wrote.

For an individual prostate cancer patient, the results reported in this analysis warrant a discussion with his clinician, wrote the editorial authors, noting that secondary malignancies can be added to the list of avoidable adverse effects associated with the treatment of men with low-risk disease who likely need no treatment. But, they emphasized, these results do not impede the use of radiotherapy for men with high-grade, lethal disease who would benefit from such anticancer treatment.