BUFFALO, N.Y. -- Isoflavones, chemicals found in soy products
and in small amounts in other plant-based foods, may be associated
with a reduced risk of developing certain types of breast tumors, a
new study by researchers at the University at Buffalo and Roswell
Park Cancer Institute has found.
The study showed that women with newly diagnosed breast cancer
who consumed the highest versus lowest amounts of isoflavones, a
class of phytoestrogens, had a 30 percent decreased risk of having
an invasive tumor -- one that had spread into the breast tissue
instead of remaining in the epithelial layer of cells -- and a 60
percent decreased risk of having a grade 1 tumor.
Tumor grade refers to the similarity of cancer cells to normal
cells. As cancer progresses, the cells become more abnormal and
increase in grade (1, 2, 3). The study results also found a
potential decreased breast cancer risk associated with specific
Anne Weaver, an epidemiology PhD student in the UB Department of
Social and Preventive Medicine, UB School of Public Health and
Health Professions, is first author on the study. She presented the
findings at the American Association for Cancer Research
International Conference -- Frontiers in Cancer Prevention held
Nov. 7-10 in Philadelphia, Pa.
"Countries with high isoflavone intake tend to have lower breast
cancer rates," according to Weaver. "Previous studies have had
mixed results, but they indicate that isoflavone intake may be
related with a reduced risk of breast cancer. This study examined
isoflavone intake in relation to several different tumor
"We believe that isoflavone intake may affect characteristics of
breast cancer in different ways, so we examined several
characteristics of breast cancer, including tumor size, stage,
grade and hormone receptor status," Weaver notes. Higher stage and
grade indicate more severe cancers, while hormone receptor status
determines how likely a tumor is to respond to hormone-based
The researchers compared the amount of isoflavones eaten by
women without cancer to the amount of isoflavones eaten by women
with different breast cancer characteristics.
The study involved 683 women with newly diagnosed breast cancer
and 611 women without a history of breast cancer, all of whom were
enrolled in Roswell Park Cancer Institute's Data Bank and
BioRepository. All women completed a questionnaire providing
biographic and dietary information. Data on tumor characteristics
of the women with cancer was retrieved from their medical
In addition to findings on isoflavones in general, results of
the analysis showed a slight to moderate decrease in cancer risk
and tumor characteristics in women in the highest third of specific
The isoflavone glycetein showed the most relationships with
breast tumor characteristics. In the highest versus lowest third,
glycetein was associated with an approximately 25 percent decreased
odds of having cancer, 60 percent decreased odds of having a grade1
tumor and 30 percent decreased odds of having a HER2 negative
HER2 is a human epidural growth factor receptor, one of the
hormone receptors, along with estrogen and progesterone receptors,
that commonly are used to diagnose breast cancer. "Generally, HER2
positive tumors are more aggressive while HER2 negative tumors are
less aggressive," explains Weaver.
In postmenopausal women only, results showed that cases in the
highest-third intake versus lowest-third intake of the isoflavone
glycetein had an approximately 30 percent decreased odds of having
luminal A, or stage I, disease. The isoflavone genistein was
associated with approximately 60 percent decreased odds of having a
grade 1 tumor.
In premenopausal women only, highest total isoflavone intake as
well as intakes of isoflavones daidzein, genistein, and glycetein
were associated with an approximately 70 percent decreased odds of
having a large (greater than 2 cm) tumor. In addition,
premenopausal women in the highest- versus lowest-third of total
isoflavones and genistein intake had an approximately 60 percent
lower risk of having stage II breast cancer.
"Results showed that premenopausal women with larger tumors were
less likely to have eaten high amounts of isoflavones, compared to
premenopausal women without cancer," Weaver notes.
"Overall, this study indicates that isoflavone intake may be
associated with tumor characteristics with more favorable
prognoses," Weaver reiterates. "However, our sample had low
isoflavone intake compared to, for example, an Asian population.
Most isoflavone intake was from other foods, so we can't comment
specifically on soy."
The results were not conclusive, Weaver notes, so further
studies need to be done to determine the mechanisms by which
isoflavones may affect tumor characteristics.
Susan McCann of Roswell Park Cancer Institute (RPCI) is senior
author on the study. Additional contributors from RPCI are Katie
Hootman (formerly a Department of Social and Preventive Medicine
student at UB), Christine Ambrosone, Helena Hwang and Carl
Morrison. Peter Horvath from UB also is a contributor.
The research is funded by grants to McCann from the National
The University at Buffalo is a premier research-intensive public
university, a flagship institution in the State University of New
York system and its largest and most comprehensive campus. UB's
more than 28,000 students pursue their academic interests through
more than 300 undergraduate, graduate and professional degree
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the Association of American Universities.