Women who are overweight or obese when diagnosed with some breast cancers have a higher risk of dying after a recurrence compared with women of normal weight, according to a U.S. study.

Obesity at the time of breast cancer diagnosis is associated with poorer survival, but less is known about  specific subtypes of the disease, and treatments might be influenced by excess weight.

si-mammogram-breast-220-cp-

The risk of breast cancer recurrence was higher among women who were overweight or obese at the time of diagnosis, according to a U.S. study released Monday. (Torin Halsey/Wichita Times Record News/Associated Press)

When the U.S. National Cancer Institute sponsored treatment trials, researchers were able to explore if increasing body fat affects breast cancer recurrence and survival.

"The results of this analysis clearly establish a relation between higher BMI at the time of breast cancer diagnosis and higher risk of recurrence and death, specifically in hormone receptor-positive, HER-2 positive disease, which accounts for about two-thirds of all breast cancers," Dr. Joseph Sparano of the Albert Einstein College of Medicine's Montefiore Medical Center, in Bronx, N.Y., and his co-authors conclude in Monday's issue of the journal Cancer.

"What remains uncertain, however, is whether dietary and lifestyle interventions resulting in weight loss after a breast cancer diagnosis could substantially reduce the risk of recurrence."

The study included 6,885 women with Stage 1 to Stage 3 breast cancer who were given chemotherapy with doxorubicin.

To participate, the women had to have normal heart, kidney, liver and bone marrow function, meaning those with significant health issues were excluded.

The stepwise relationship between increasing body mass index and poor outcomes applied only to hormone receptor–positive breast cancers, not HER-2/neu-overexpressing or triple-negative types, the researchers found.

For hormone-receptor positive patients, obesity was associated with 1.31 or about 30 per cent higher risk of recurrence, the researchers found.

"Treatment strategies aimed at interfering with hormonal changes and inflammation caused by obesity may help reduce the risk of recurrence," Sparano said in a release.

Researchers hope that by understanding the relationship between obesity, tumour-related factors and breast cancer subtypes, they'll be able to tell what factors contribute to recurrence and perhaps manage the disease better.

Insulin, weight and breast cancer 

Previous studies have suggested that obesity is associated with poorer outcomes for other types of breast cancer, said Dr. Pamela Goodwin, a medical oncologist at Toronto's Mount Sinai Hospital who researches the impact of lifestyle factors on breast cancer patient survival rates.

Goodwin's research suggested high insulin levels accompanying obesity encourage tumour growth, and increase the likelihood of breast cancer recurrence.

Researchers are investigating how physiological factors like insulin, estrogen and inflammation could be associated with cancer growth.

"Most women who are diagnosed with breast cancer are given advice by their oncologist to try to be physically active, to try to have their weight in an ideal range," Goodwin said.

It's becoming clear that women may not need to lose weight down to the normal range to gain health benefits.

"There's some evidence that for every one per cent of weight you lose, your insulin level, your estrogen level, your markers of inflammation will go down three per cent," Goodwin said. "So it's very encouraging."

Canadian study recruits women

Goodwin's team adapted a U.S. diabetes prevention program that included 20 phone calls to help women with breast cancer to lose weight.

Over about a month, women gradually increased their level of physical activity to at least 150 minutes a week, such as brisk walking, while they received support and troubleshooting support on making and maintaining the diet and physical activity changes.

In the pilot study of 350 women, the weight loss was maintained for the most part. But the two-year study didn't include enough women to assess breast cancer outcomes.

Goodwin and the Kingston, Ont.-based New Investigator Clinical Trials group are now recruiting women across North America to test if giving women with breast cancer regardless of their weight the diabetes drug metformin improves outcomes.

With files from CBC's Amina Zafar