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Obesity
(March 2006)
There are so many good reasons for not being overweight ...
and reducing prostate cancer aggressiveness and disease progression is one
of them. Multiple studies of large data bases confirm that as obesity
increases so does Gleason grade at diagnosis; and that PSA failure after
treatment occurs sooner; and that obesity is associated with a higher
prostate cancer mortality. In short, obesity is an independent predictor
of adverse outcome after treatment. It has not been established that
prostate cancer incidence is higher in obese men. Instead, the implication
is that obesity is associated with greater disease aggressiveness and
faster progression, and not cancer initiation.
It has not been shown that weight loss after
diagnosis improves survival, but by implication maintaining an optimal
weight in the years that might precede a diagnosis a man improves his
chances for having a less aggressive cancer. A report from M.D. Anderson (Clin
Cancer Res, 2005 Oct) found that “men who gained weight at the greatest
rate (>1.5kg/yr) between 25 years and diagnosis progressed significantly
sooner (mean time 17 months) than those who exhibited a slower weight gain
(mean time to progression, 39 months, P=0.005)”. A good primer on this
topic is “Impact of Obesity on Prostate Cancer Recurrence After Radical
Prostatectomy: Data from CaPCURE”, Bassett et al. UROLOGY 66, 2005.
The basic biologic cause of this relationship of obesity
and worse outcome is not understood. Possible etiologies are
obesity-induced alterations of sex hormones; increased insulin-like growth
factor 1 and leptin, which both increase cellular proliferation; or
obesity’s association with lower testosterone levels, which seemingly
paradoxically are related to a worse pathologic stage.
This issue is becoming increasingly important as the US
population fattens - 31% of American adults older than 20 years are obese.
The conventional measure of “fatness” is the Body Mass Index (BMI) and a
mass greater than 35 kg/m2 is considered “very obese” and less than 25
kg/m2, “normal”. The Bassett article found that at a BMI of 30 - 35 kg/m2
the risk of recurrence was 1.31 times that of lesser mass, and a BMI of >
35 kg/m2 increased risk by 1.69 times. A chart for calculating BMI is
found at http://consumer.gov/weightloss/bmi.htm. An example: a 5’11” man
weighting 250 pounds has a BMI of 35 kg/m2, whereas at 179 pounds the BMI
is 25 kg/m2.
Maintaining an optimal weight lessens
the likelihood of prostate cancer aggressiveness at diagnosis, and if the
cancer recurs, obesity at diagnosis portends a more rapid disease
progression.
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