Obesity is considered a risk factor for breast cancer, and women who are obese at time of diagnosis tend to have more aggressive disease and a poorer prognosis. However, scientists have been unsure of the basis for the correlation. The current work may close that gap in understanding.

"These findings may explain why weight gain, which is accompanied by higher than expected leptin concentrations, also has been associated with increased breast cancer risk," said Margot Cleary, Ph.D., senior author. "Preventive measures need to be taken to control these deadly diseases."

The team of basic scientists and clinicians showed that leptin enhanced anchorage-dependent proliferation in cell culture of both normal and malignant human breast epithelial cells. In the presence of leptin, the number of malignant breast cells increased 138 percent compared with an increase of 50 percent for normal breast cells. In contrast, leptin increased anchorage-independent growth considerably (by 81 percent) in the cancerous cells, but leptin had no effect on the normal cells. The latter findings may provide a partial explanation for the link between obesity and the tendency of cancers in obese women to metastasize early in the course of disease.

Cleary said that future studies should focus on determining whether the presence of leptin receptors in breast tumors is associated with other factors commonly assessed during breast cancer diagnosis such as presence or absence of hormonal receptors.