Obesity was not associated with breast cancer risk in Mexican-American women, even when measured at numerous ages throughout a woman’s lifetime, according to data presented at the Ninth Annual AACR Frontiers in Cancer Prevention Research Conference, held here Nov. 7-10, 2010.

However, data did show that weight gain during adulthood seemed to reduce breast cancer risk, regardless of menopausal status.

“We found that for every 5 kg of weight gain there was a significant 8 percent decrease in the risk for breast cancer,” said Krystal Sexton, Ph.D., a Susan G. Komen Fellow in breast cancer disparities research at The University of Texas Health Science Center at Houston School of Public Health. “However, it is important that we do not send a message that gaining weight prevents breast cancer.”

Instead, Sexton and colleagues in the department of epidemiology at The University of Texas MD Anderson Cancer Center, are hypothesizing that the reduced risk for breast cancer among overweight and obese Mexican-American women may be due to a shorter lifetime exposure to estrogen, which is associated with breast cancer.

Previous research has shown that in Mexican-American women there is an association between obesity and earlier age of menopause.

“Women in our study who did not have breast cancer were actually experiencing menopause at an earlier age — especially women who were overweight and obese — compared with women who were overweight and obese and did have breast cancer,” Sexton said.

This earlier onset of menopause exposed overweight and obese women to two fewer years of estrogen throughout their lifetimes, possibly putting them at a lower risk for breast cancer, according to Sexton.

The researchers identified 155 Mexican-American women with breast cancer and compared them with 333 women of similar ages without breast cancer. Patients reported their weights at ages 15, 30 and at cancer diagnosis. They also reported weight gain between age 15 and diagnosis.

Unlike research in non-Hispanic white women, which has shown an increased risk for breast cancer in obese postmenopausal women, there was no association between body mass index and breast cancer in Mexican-American women, regardless of menopausal status.

“We know that Hispanic women have a lower incidence of breast cancer, but they continue to be diagnosed with breast cancers that have larger tumor sizes, more advanced cancer stages and poorer prognostic factors, leading to lower survival rates compared to non-Hispanic white women,” Sexton said. “There is a real need to continue to try to understand why these disparities exist.”

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