Blood leptin level may be a useful risk marker for breast cancer, according to a presentation published in the Proceedings for the 2003 Annual Meeting of the American Association for Cancer Research.

Findings from a small study suggest that measurement of leptin levels may offer more prognostic information than simply measuring body mass index and current dietary fat intake because leptin may reflect a patient’s history of fat intake. Because increased fat is associated with increased bioavailable estrogen, "measuring leptin could be an additional marker for assessing [estrogen-related] breast cancer risk," said lead author, Richard Hajek, Ph.D.

"None of these measures are perfect, but the amount of leptin found in a woman's blood stream can indicate her accumulation of fat over the years," he said. "Measuring current body weight and fat intake doesn't offer that kind of perspective."

Leptin is a hormone produced by fat tissue that signals satiety within the brain. In general, as body fat increases, more leptin is produced and appetite is less. Conversely, as body fat decreases, less leptin is produced and appetite is stimulated.

According to Hajek, leptin levels can change in response to a pattern of eating. For example, a thin woman with a low leptin level who eats a higher fat diet for weeks or months (with a corresponding increase in body fat) will produce a higher level of leptin. If she returns to her normal eating pattern, her leptin level will fall but may not return to baseline level.

Thus, a researcher would see a woman with a relatively low body fat index and a low current fat intake --- but leptin testing might suggest that there had been a period of higher fat intake and higher estrogen levels (and thus, the possibility of a period of increased risk for breast cancer).

In the current study, researchers studied 38 postmenopausal women to evaluate changes in leptin levels between women who started a high-fiber, low-fat diet and women who started high-fiber diet with no modification in fat intake. The investigators found that, if body weight and body fat together were not considered, there was a correlation between leptin and diet. As women ate fewer grams of fat, their leptin levels decreased.

One study limitation was the high proportion of overweight women (with resultant high baseline leptin levels). Despite differences in baseline leptin levels, volunteers who ate more fiber and less fat reduced their leptin levels and some lost a little weight.

Hajek believes further study of breast cancer risk factors over the lifetime --- including long-term fat intake, body mass index, leptin level, and estimated bioavailable estrogen --- will enable physicians to improve estimation of an individual’s risk.