Obesity Linked to Prostate Cancer After Radiation

Obesity Linked to Prostate Cancer After Radiation
Records of Patients With Localized Tumors Studied

Obesity is a predictor of whether prostate cancer that has not spread beyond the prostate will progress following radiation therapy, according to a study published in the Aug. 1 issue of the journal Cancer.

The report by M. D. Anderson researchers, involving an analysis of 873 patient records, suggests that obese prostate cancer patients should be followed more closely after treatment, says the study's principal investigator Sara Strom, Ph.D., an associate professor in M. D. Anderson's Department of Epidemiology.

"When patients and their physicians are uncertain about the need for further therapy, our research indicates that a man's weight should be factored into that decision," she says.

Study description: Patient records examined

Scientists examined the records of 873 patients whose prostate cancer was confined within the prostate and who were treated with radiotherapy at M. D. Anderson between 1988 and 2001. Of these patients, 18% were mildly obese and 5% were moderately to severely obese.

Researchers determined obesity based on body mass index (BMI), the measure of body fat in relation to a person's height and weight.

Researchers cited these BMI categories:

Normal weight= 18.5 - 24.9
Overweight= 25 - 29.9
Mildly obese= 30.0 - 34.9
Moderately and severely obese= BMI of 35 or greater

( BMI can be calculatedthrough the National Institutes of Health website.)

Primary results: Obese patients at greater risk

According to the study:

Moderately and severely obese patients- had a 99% greater risk of developing "biochemical failure" [a rising prostate specific antigen (PSA) level], which can indicate advancing cancer.

Mildly obese patients- had a 66% increased risk of having a tumor that recurs or that spreads to other parts of the body compared to non-obese patients.

After an average follow-up period of 96 months, 295 patients experienced a rising PSA, and cancer recurred in 127 patients.

Additional results: Obese patients diagnosed at earlier age

Researchers found that patients who were obese tended to be diagnosed with prostate cancer at an earlier age than patients who were not obese, and also that African-American men had the highest obesity rates.

Background: Results affirm previous study

The study is the first to examine the relationship between obesity and prostate cancer progression after primary therapy with external beam radiation therapy, a common treatment option, Strom says.

The finding mirrors results from a parallel study by M. D. Anderson researchers reported last year in Clinical Cancer Research, which found that a history of weight gain or obesity at the time of diagnosis also played a role in how aggressive prostate cancer may become after treatment with surgery.

What's next: Strategies to prevent further disease

In the current study, after adjusting for clinical and treatment variables among patients, researchers found that BMI significantly predicted whether a patient would experience both rising PSA and a return of prostate cancer.

Strom and her colleagues cannot yet say why excess BMI contributed to cancer progression, or whether losing weight after prostate cancer diagnosis will make any difference in outcome. "But by knowing this association, we may be able to design rational preventive strategies," she says.

- From staff reports