Soy isoflavone intake decreases risk of invasive breast tumor

Increased phytoestrogens commonly found in dietary soy may modify the risk of some types of breast cancer, according to findings presented at the Ninth Annual AACR Frontiers in Cancer Prevention Research Conference, held Nov. 7-10, 2010.

"This study was unique in that we looked at specific subtypes of breast cancer, and found a suggestion that menopausal status may play a role in risk," said Anne Weaver, a graduate student at the University at Buffalo and research apprentice at Roswell Park Cancer Institute.

Weaver and colleagues evaluated 683 women with breast cancer and compared them with 611 healthy women. Dietary data patterns were observed using a food frequency questionnaire and isoflavones were measured as a dietary, rather than supplemental, intake. Isoflavone intake was divided into three groups.

Those women with the highest isoflavone intake had an approximately 30 percent decreased risk of having an invasive breast tumor, and an approximately 60 percent decreased risk of having a grade 1 tumor.

Observations by menopausal status revealed the following: Among premenopausal women, the highest intake of isoflavones had a 30 percent decreased risk of stage I disease, a 70 percent decreased risk of having a tumor larger than 2 cm, and a 60 percent decreased risk of having stage 2 breast cancer. These connections were not seen among postmenopausal women.

Like most dietary studies, Weaver said these findings are not definitive and need to be considered in the context of further follow-up and confirmation.

"Still, we definitely saw a reduction that deserves further investigation," she said.