Obese men have an increased risk of cancer recurrence after undergoing treatment with radiotherapy for localized prostate cancer, new research shows.

The findings “suggest a link to the biologic basis of tumor progression that can be therapeutically exploited,” lead author Dr. Sara S. Strom, from the M. D. Anderson Cancer Center in Houston, and colleagues note.

Previous reports have linked obesity with an increased risk of biochemical failure - treatment failure determined by laboratory tests - after prostate surgery. However, it was unclear if the same held true for men treated with radiotherapy.

The study, reported in the current online issue of the journal Cancer, involved 873 men who underwent radiation treatment as their only treatment for localized prostate cancer between 1988 and 2001.

Obesity was determined by an elevated body mass index (BMI), a ratio of height to weight commonly used to determine if a person is overweight or underweight. The researchers found that 18 percent of the men were mildly obese and 5 percent were moderately to severely obese.

Obese patients were more likely to be a younger age at diagnosis, to have a more recent diagnosis, and to be African-American.

After an average follow-up period of 96 months, 295 men experienced biochemical failure and 127 had full disease recurrence with symptoms.

Additional analysis revealed that obesity was a statistically significant independent predictor of both biochemical failure and disease recurrence. Moreover, as the severity of obesity worsened, the risk of these negative outcomes increased.

For example, mildly obese men had a 55-percent higher risk of biochemical failure and moderately-to-severely obese men had a 99-percent higher risk compared with normal-weight men. Similarly, the corresponding increases for prostate cancer recurrence were 65 percent and 66 percent.

The researchers say the findings underscore the importance of obesity in prostate cancer progression. Understanding the mechanism involved, they hope, “will lead to rationally designed preventive strategies.”

Cancer, June 26, 2006.