Obesity Linked to More Aggressive Tumors
Summary: Men who lose weight in adulthood seem to lower their risk of getting aggressive prostate cancer, according to a new American Cancer Society study. The study is the first to link weight loss to a reduced risk of this disease.
Why it's important: Prostate cancer is the most common cancer (other than skin cancer) among men in the US. More than 234,000 men are expected to develop prostate cancer in 2006, and some 27,000 are expected to die from it. Although most men who get prostate cancer survive the disease, its treatments can cause side effects like impotence and incontinence that can reduce quality of life. The new finding suggests that losing weight -- or never gaining it in the first place -- may be one way to reduce the toll prostate cancer takes.
What's already known: Many previous studies have examined the link between excess weight and prostate cancer. Several of those have found that heavier men -- those with a high body mass index (BMI) -- are more likely to be diagnosed with more advanced prostate cancer and more likely to have a recurrence of the disease after treatment than are men of normal weight. But it wasn't clear whether losing weight would have an impact on the development of prostate cancer.
How this study was done: The new study followed nearly 70,000 men who were part of a larger American Cancer Society lifestyle study called the Cancer Prevention Study II, which began in 1982. The men answered periodic questionnaires about their habits (diet, exercise, smoking, etc.) and reported their height and weight, which were used to calculate BMI. The researchers analyzed the relationship between BMI and different types of prostate cancer in men who developed the disease between 1992 and 2003. The results were published in the journal Cancer Epidemiology, Biomarkers & Prevention.
What was found: More than 5,000 men developed prostate cancer between1992 and 2003. Men with higher BMI had a higher risk of developing high-grade (more aggressive) prostate cancer, though their risk of developing low-grade prostate cancer decreased. Heavier men also had a higher risk of developing metastatic or fatal prostate cancer.
But men who lost at least 11 pounds between 1982 and 1992 had a lower risk of developing prostate cancer, especially high-grade cancer, compared to men whose weight stayed within 5 pounds of what it was in 1982.
The researchers say several factors could be causing this effect. It may have to do with the way obesity affects testosterone or insulin levels in the body. Or it may be that obese men don't get screened as often (screening was lower among heavier men in the study), so their prostate cancers are detected later. Obese men also tend to have lower PSA levels, which may obscure prostate cancer until it is more advanced. They also have larger prostates, which makes finding cancer with a biopsy harder to do.
The bottom line: Weight is one of the most common cancer risk factors that people have the ability to control, says lead study author Carmen Rodriguez, MD, MPH, an American Cancer Society epidemiologist.
"Our study adds to increasing evidence of the importance of maintaining a healthy weight throughout adult life," she explains. "Although our study suggests that weight loss may lower the risk of aggressive prostate cancer, given the difficulty of losing weight, emphasis should be put on the importance of avoiding weight gain to reduce the risk of prostate cancer."
Citation: "Body Mass Index, Weight Change, and Risk of Prostate Cancer in the Cancer Prevention Study II Nutrition Cohort." Published online Dec. 20, 2006, in Cancer Epidemiology, Biomarkers & Prevention. First author: Carmen Rodriguez, MD, MPH, American Cancer Society.
