NEW YORK (Reuters Health) - Women who gain the most weight over their lifetime are most likely to develop breast cancer after menopause, new study findings from Canada suggest.

"Gaining weight over a lifetime increases breast cancer risk," Dr. Christine M. Friedenreich of the Alberta Cancer Board in Calgary told Reuters Health.

"Being overweight after menopause is also a risk factor," she said. Extra pounds seem to be particularly risky when they are carried around the abdomen, the Canadian researcher noted.

A woman's shape and weight have been thought to influence her risk of breast cancer, but the evidence has not been conclusive. To evaluate the possible connection, Friedenreich and her colleagues compared 1,233 women with breast cancer and a "control" group of 1,237 women who did not have the disease.

Among premenopausal women, none of the so-called anthropometric factors--waist circumference, waist-to-hip ratio and weight gain during adulthood--affected the risk of cancer, according to a report in the International Journal of Cancer.

But a woman's shape and weight did affect the risk of breast cancer after menopause. Women with the highest waist-to-hip ratio, meaning that they carried more weight around the abdomen, were 43% more likely to have breast cancer than women with the lowest ratio.

Gaining weight as an adult also seemed to make women more susceptible to breast cancer, the report indicates. Women who gained the most weight since age 20 (25 kilograms, or about 55 pounds, or more) were 35% more likely to develop breast cancer than those who had gained the least (less than 7.8 kg, or about 17 pounds).

The effects of hormone replacement therapy on the risk of breast cancer are controversial, but the present study suggests that hormone therapy may diminish some of the increased risk brought about by weight gain or extra pounds around the waist. The link between all measures of body weight and size and the risk of cancer was stronger in women who had never used hormone replacement therapy, according to the report.

Although Friedenreich and her colleagues call for additional research, they conclude, "Our results corroborate and strengthen the evidence from previous research that avoiding weight gain throughout life is a means of reducing postmenopausal breast cancer risk," especially among women who have never taken hormone replacement therapy.

SOURCE: International Journal of Cancer 2002;99:445-452.

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