Obesity associated with less favorable outcome after radiation therapy for prostate cancer

Obese men with prostate cancer are at higher risk for treatment failure after primary radiation therapy, according to a new study.

Published in the August 1, 2006 issue of CANCER, a peer-reviewed journal of the American Cancer Society, the study reveals that each incremental increase in body mass index (BMI) increased the risk for clinical or biochemical failure. The study is the first to investigate the association between obesity and post-radiotherapy outcome.

Evidence has increasingly shown that obesity has a deleterious effect on the human body, from the risk of diabetes to joint disease. Obesity has more recently been shown to play a significant role in the development of some cancers, including cancers of the breast, prostate, colon, and many others. Obesity has also been associated with the progression of disease. Obese men with prostate cancer often have more aggressive disease and higher mortality rates. Researchers postulate that fat tissue influences concentrations of various significant signaling molecules, such as testosterone, estrogen, insulin and insulin-like growth factor, which play a role in prostate cancer development and progression.

There is already a body of scientific evidence demonstrating that obesity is linked to treatment failure after prostatectomy. However, there are no data on the effects of obesity on the effectiveness of radiation treatment for prostate cancer. Sara Strom, Ph.D. of the University of Texas M. D. Anderson Cancer Center in Houston and colleagues reviewed the medical records of 873 patients who received radiotherapy alone for prostate cancer. Among the group, 18 percent were mildly obese and 5 percent were moderately to severely obese.

After an average 96 months of follow-up, 295 of the men had three consecutive increases in blood PSA, indicating biochemical failure. Meanwhile, 127 of the men had clinical failure (local recurrence and/or distant metastasis) determined by radiologic studies, biopsy, or physical examination. On analysis, risk of biochemical and clinical failure were influenced by BMI. As BMI increased, the risk of disease progression following therapy also increased. For example, men who were moderately or severely obese were at double the risk for biochemical failure than other men who were not.

The authors conclude, "our findings validate the importance of obesity in prostate cancer progression and suggest a link to the biology of this tumor."

To understand the influence of obesity on treatment and possibly exploit that understanding to improve treatment outcome, "future studies should evaluate the relationship of obesity with dietary factors, genetic modifiers of steroid androgen metabolism, insulin, and a detailed investigation of the insulin growth factor pathway to explore the underlying mechanisms of action in prostate carcinogenesis," suggest the authors.

Article: "Influence of Obesity on Biochemical and Clinical Failure after External-Beam Radiotherapy for Localized Prostate Cancer," Sara S. Strom, Ashish M. Kamat, Stephen K. Gruschkus, Yun Gu, Sijin Wen, Min Rex Cheung, Louis L. Pisters, Andrew K Lee, Charles J Rosser, Deborah A. Kuban, CANCER; Published Online: June 26, 2006 (DOI: 10.1002/cncr.22025); Print Issue Date: August 1, 2006.

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