Obesity hikes cancer risk

2004-08-24 11:56

Washington - Heart disease and diabetes get all the attention, but expanding waistlines increase the risk for at least nine types of cancer too.

With the obesity epidemic showing no signs of waning, specialists say they need to better understand how fat cells fuels cancer growth so they might fight back.

What's already clear: Being overweight can make it harder to spot tumours early, catch recurrences, determine the best chemotherapy dose, even fit into radiation machines.

That in turn hurts chances of survival. A major study last year estimated that excess weight may account for 14 to 20% of all cancer deaths - 90 000 a year.

"Obesity makes taking care of cancer patients much more complicated," says Dr Christopher Desch, a medical oncologist in Richmond, Virginia.

So why is cancer often the afterthought when listing obesity's multiple risks?

"The cancer picture is a little bit more subtle," says American Cancer Society epidemiologist Eugenia Calle, one of the nation's leading specialists on the link.

Cancer develops more slowly

The risks of heart disease and diabetes from packing on kilos are much higher, and more immediate because cancer typically develops more slowly than those illnesses, she explains.

But with nearly two-thirds of US adults now overweight plus an ageing population - cancer is predominantly an older person's disease - oncologists want more attention to the link.

Fat is known to increase the risk of developing cancers of the colon, breast, uterus, kidney, oesophagus, pancreas, gallbladder, liver and top of the stomach.

How big a role girth plays varies greatly, and the strongest connections are actually in less common cancers.

Weight is most strongly linked to cancer of the uterine lining, or endometrium. An overweight woman has twice the risk of developing that cancer as a lean one; once she becomes obese, the risk rises as much as 3.5 to 5-fold.

The obese have up to triple the risk of kidney cancer and a type of oesophageal cancer as do the normal-weight.

The risk is somewhat smaller among two of the nation's most common cancers - overweight or obese men are 50% to twice as likely as lean men to get colon cancer. For women, the extra risk is 20 to 50%. No one can yet explain the gender difference.

Fat is linked to breast cancer in postmenopausal women only, increasing risk of the disease by 30% among the overweight and 50% among the obese.

For the other four cancers, the obesity risk falls somewhere in between.

The reason for the variation: Fat cells apparently play different roles that can spur different types of cancer growth.

But exactly how fat cells work isn't well understood. They can spur surges of insulin and proteins that may in turn unleash out-of-control growth among certain cell types.

- AP