[al from Canada]

May 21 (foodconsumer.org) - Postmenupausal women who gain weight in adulthood face a higher lifetime risk of all types of breast cancer, particularly those most dangerous forms of the disease, according to a new study.

Published in the July 1, 2006 issue of Cancer, the study reveals that the greater the weight gain as an adult, the greater the risk for breast cancer of all types in terms of histological types, tumor stages, and grades, particularly advanced malignancies.

Women who gained over 60 pounds were up to three times more likely to have breast cancer spread than women with less weight gain, a finding that has not been reported before. This is in agreement with a previous finding that obesity increases risk of dying from breast cancer.

Breast cancer risk was about 70 percent higher in women with a weight gain of 21 to 40 pounds and 1.8 times greater in women who gained between 41 and 60 pounds.

Obesity has been well associated with breast cancer risk in previous studies, but there is no data on whether that risk is specific for the type of the disease.

The study, led by Heather Spencer Feigelson, Ph.D., M.P.H of the American Cancer Society, looked at the link between weight gain and type of invasive breast cancer among 44,161 postmenopausal women who were not taking hormone therapy.

The researchers found that the greater the weight gain, the greater the risk for all types, stages, and grades of breast cancer, especially for late-stage cancer or cancer that had spread to other parts of the body.

Compared to women who gained 20 pounds or less during adulthood, women who gained over 60 pounds were almost twice as likely to have ductal breast cancer and more than 1.5 times more likely to have lobular type breast cancer, according to the study.

The risk for metastatic breast cancer increased for all women who gained weight, with the risk greater than three-fold for women who gained over 60 pounds.

Weight gain is expected to increase the risk of estrogen receptor positive breast cancer only. But there are many other theories to explain the effect of weight gain on breast cancer.

According to the estrogen theory, with fat tissue the primary source of estrogen, the hormone levels in postmenopausal women are 50 to 100 percent higher among heavy women than lean women. Estrogen-sensitive tissues are therefore exposed to more estrogen stimulation in obese women, leading to a more rapid growth of estrogen-responsive breast cancer.

The effect of obesity on breast cancer risk depends on a woman's menopausal status. Obese postmenopausal women have 1.5 times the risk of women of a healthy weight compared to those with a healthy weight whereas obese women somehow have a lower risk of developing breast cancer, earlier studies found.

Obesity can also increase risk of death from breast cancer in postmenupausal women compared with lean women.

The distribution of body fat may also affect breast cancer risk, previous studies have found. Women with a large amount of abdominal fat have a greater breast cancer risk than those whose fat is distributed over the hips, buttocks, and lower extremities.

The current weight is not as important as a woman's weight gain from the age of 18, the researchers say.

"these data further illustrate the relationship between adult weight gain and breast cancer, and the importance of maintaining a healthy body weight through-out adulthood," Dr. Feigelson and colleagues conclude.

In the United States, 220,000 new cases of breast cancer are diagnosed each year. Among them, scientists estimate 41,000 new cases or about 11,000 to 18,000 deaths per year from breast cancer can be avoided if women maintain a healthy weight throughout their adult lives.

An estimated 64 percent of U.S. adults are either overweight or obese, according to the 1999-2000 National Health and Nutrition Examination Survey (NHANES). Obesity is believed to be responsible for 3.2 percent of all new beast cancer cases diagnosed each year.

Excess weight gain is also linked with many other types of cancers, according to earlier studies. It is estimated that 20 to 30 percent of cancer cases including breast cancer are associated with obesity.

Preventing weight gain can reduce the risk of many cancers including postmenopausal breast cancer, earlier studies have found. Experts recommend that people establish habits of healthy eating and physical acti