Does Radiation Treatment for Prostate Cancer Heighten MDS Risk?

A Cleveland Clinic study has found that men who undergo therapeutic radiation treatment for prostate cancer have no greater risk of developing myelodysplastic syndromes (MDS) than the general population.

Senior study author Mikkael A. Sekeres, MD, MS, of the Department of Hematologic Oncology and Blood Disorders in Cleveland Clinic’s Taussig Cancer Institute, says the findings came as a surprise.

Delivery of external beam radiation to the prostate inadvertently irradiates the surrounding pelvic bones, which are estimated to contain more than half the body’s reserve of active bone marrow mass.

“The medical community had long assumed that patients who received radiation therapy to treat prostate cancer were at a higher risk for developing MDS,” Dr. Sekeres says. “The reason for that is quite simply geography, since the prostate is right in the middle of the pelvis, and the pelvis is a major site of bone marrow production in the body.”

Study Details

The study, published recently in the Journal of the National Cancer Institute, was a joint effort between Taussig Cancer Institute and the Glickman Urological & Kidney Institute. The retrospective cohort analysis was based on data from 10,924 prostate cancer patients who were treated at Cleveland Clinic from 1986 to 2011 with either surgery, radiotherapy with external beam radiation (EBRT), or radiation therapy with brachytherapy.

A total of 31 cases of therapy-related MDS were observed during the study period. In multivariable analyses, MDS rates were similar in patients who underwent surgery for prostate cancer compared with those who received some type of radiotherapy. The MDS rates observed in the study were found to be comparable to rates in population-based registries, including the Ohio Cancer Incidence Surveillance System (OCISS) and the Surveillance, Epidemiology, and End Results (SEER) database.

Advancing age is an independent risk factor for developing MDS, which the study analyses confirmed.

Clinical Significance

MDS is the most common bone marrow failure condition in the United States, with an age-adjusted incidence rate of 4.4 per 100,000 people. The majority of cases are spontaneous, but approximately 14 percent are considered therapy-related, occurring in cancer patients on average five to seven years after treatment with cytotoxic chemotherapy, radiation or both.

Exposure to ionizing radiation had been linked to subsequent development of MDS in several cancer cohorts. But until this study, the risk of MDS in prostate cancer patients treated with therapeutic radiation had remained unclear.

“What’s been problematic is that when an older man who has a history of receiving radiation for prostate cancer develops MDS, the radiation has been viewed as the cause for MDS — when it most likely was unrelated,” Dr. Sekeres explains. “Based on the results of our study, patients receiving radiation for prostate cancer can rest assured that they do not have excess risk for developing MDS within their lifetime.”

As patients were collected over a 25-year period, follow-up was limited. However, given the median patient age of 64 and average life expectancies, Dr. Sekeres says any influence that therapeutic radiation for prostate cancer might or might not have beyond the study’s follow-up period would likely be “clinically meaningless.”

Photo by Russell Lee.