Prostate Cancer

There are many studies that do not support an association between body mass and incident prostate cancer (18,34-36,173), although four large recent studies found a small but statistically significant increased risk of prostate cancer among obese men (131,132,174) or a significant trend toward increasing risk with increasing BMI (96). In addition, there is accumulating evidence that obesity is associated with an increase in risk of advanced prostate cancer or death from prostate cancer (175-181). Recent studies consistently indicate that obese men with prostate cancer are more likely to have aggressive disease that recurs after radical prostatectomy than nonobese men (182-184).

As with breast cancer, "nonbiological" issues of screening, detection, and treatment are important to the evaluation of the impact of adiposity on prostate cancer prognosis. It can be harder to perform a digital rectal examination in obese men because of their general adiposity in combination with larger prostate size (181). Additionally, despite larger prostate sizes, obese men may have lower serum levels of prostate-specific antigen (PSA) (185-187), potentially biasing them toward later stage at diagnosis even in the presence of PSA screening. Surgery is more difficult to perform in obese men, with a greater risk of positive surgical margins (181). Still, mortality from prostate cancer was found to be increased in obese men in a prospective cohort study conducted from 1950 to 1972 (177), long before PSA screening, and at a time when surgery was rarely done, suggesting that the adverse impact of adiposity on prognosis is rooted in biological characteristics of the tumor.

Several studies suggest that insulin, which is strongly correlated with obesity, acts to promote prostate cancer development and growth (188-191). Increased levels of circulating leptin, also correlated with adiposity, have been found in two studies to be associated with larger, more advanced, higher-grade tumors (192,193), although a third study did not confirm this finding (194). Decreased adiponectin levels have also been linked to high-grade, advanced prostate cancer (195).

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