So says a study in the August issue of the journal Cancer.
The study comes from researchers at Houston's University of Texas M.D. Anderson Cancer Center. They included Sara Strom, PhD.
Strom's team found that external radiation therapy worked for most of the 873 prostate cancer patients they studied. However, the therapy was 4% to 5% more likely to fail in the study's relatively few obese men.
Prostate Cancer Study
Of the 873 patients in Strom's study:
- All were treated at the cancer center between 1988 and 2001.
- Their cancer hadn't spread beyond the prostate at the time of treatment.
- Ages ranged from 41 to 84 (average age was mid-to-late 60s).
- Most were white.
- 18% were mildly obese, with body mass index (BMI) of 30 to 34.9.
- 5% were moderately to severely obese, with BMI of at least 35.
The men received external radiation therapy as their only prostate cancer treatment. None got surgery or internal radiation therapy, in which radioactive "seeds" are implanted in the cancerous area.
Black patients had the highest obesityrates. Obesity was also associated with younger patients.
After Radiation Therapy
The researchers followed the men for an average of eight years. During that time, the men got regular checkups that included measuring height, weight, and blood levels of prostate-specific antigen (PSA).
PSA is made by the prostate gland. High levels of the chemical may indicate prostate cancer, but can also signal benign prostate problems. In men with prostate cancer, PSA, a chemical made by the prostate gland, is often used to monitor disease during or after treatment.
After radiation, the men's PSA levels fell, as expected. But during the follow-up period, PSA levels rose on three consecutive tests for 295 men. Those patients had "biochemical failure" of radiation therapy, write Strom and colleagues.
Biochemical failure didn't always mean the prostate cancer returned. However, 127 of the 295 patients with increasing PSA levels had a recurrence of prostate cancer during the follow-up.
After adjusting for other risk factors, the researchers found that obese patients were 4% more likely to have a biochemical failure of external radiation therapy and 5% more likely to have a recurrence of prostate cancer during the study.
The study doesn't prove obesity caused radiation therapy to fail in any of the men. As an observational study, the results can't show cause and effect. Also, the study didn't look at men who got radiation therapy in addition to other prostate cancer treatments.
It's not clear why or how obesity affects the chances of success with external radiation therapy for prostate cancer. It will take more work to figure that out, write Strom and colleagues.