Leptin protein hints at link between obesity and cancer

Dylan Thomas

A protein associated with weight gain has been shown to spur the growth of breast cancer cells, shedding even more light on a link between obesity and cancer.

Margot Cleary, the University scientist who conducted the research, said the findings provide more evidence that maintaining a healthy body weight is important for many health reasons.

Leptin, the protein Cleary studied, is made in fat tissue. Researchers think it might be secreted in proportion to the amount of body fat a person has.

The research, conducted at the University’s Hormel Institute in Austin, Minn., used breast cancer cells and normal mammary cells. Both types of cells contain leptin receptors, which receive leptin and signal cell growth.

In both cases, the cells grown in the presence of leptin increased in number. However, the breast cancer cells increased 150 percent, compared with 50 percent among the normal cells, Cleary said.

Early research on leptin focused on its function in the brain. Because the amount of leptin present in a body is proportionate to the amount of body fat, researchers hypothesized that its function was to tell the brain to eat less.

But on the cellular level, researchers have found leptin actually encourages cell growth.

Cleary hypothesizes that leptin is not a breast cancer risk unless a woman is overeating. Then, perhaps when the amount of leptin in the body reaches a threshold, it might trigger cell growth that leads to tumors, a hypothesis that is supported by evidence from medical testing on animals.

If the findings are supported by more evidence, they could lead to a greater focus on a healthy body weight in breast cancer prevention. It might also lead to a leptin test that would assess breast cancer risk, or even cause clinicians to re-evaluate some treatments, Cleary said.

“Some of these treatments that women are receiving once they’re diagnosed with breast cancer are actually resulting in weight gain,” Cleary said. She said there needs to be more aggressive oversight of treatments.

Another possibility could be developing a drug to interfere with leptin or leptin receptors for obese women at high risk for breast cancer.

Cleary said the next step is to see if the amount of leptin levels in the body can indicate the risk level for breast cancer, or if there are other factors that are related to high leptin levels and breast cancer.

The research Cleary is doing with animals – the current research not cited in her paper – indicates obese mice get tumors at a much younger age than other mice.

However, Cleary said research might find that leptin is just one part of the link between obesity and breast cancer.

Doug Yee, program leader at the University’s Cancer Research Center, said most risk factors for breast cancer among healthy women are related to “estrogen action.” He also said estrogen levels are higher among obese women.

Further research might show that while leptin is a factor in

higher risk for breast cancer, estrogen and other hormones all play a role.

“There have been a handful of hormonal factors that are related to breast cancer risk, and they’re probably all interlinked,” Yee said.

Yee said studies show that while obesity might be some indication of increased risk for breast cancer, things such as family history, the age a woman first menstruates or becomes pregnant are all more strongly associated with a risk for breast cancer.

“Even though obese women are Ö more prone to develop breast cancer, it’s not such a strong risk factor that it’s commonly used in clinical models,” Yee said.

Still, if additional research supports Cleary’s findings, both she and Yee agree it will be just another reason encouraging people to maintain their ideal body weight.

“If we can present a united and definite front that maintaining weight or losing weight definitely is going to have some kind of positive outcome, I think people are more likely to take it seriously,” Cleary said.

Dylan Thomas welcomes comments at [email protected]