Women who have survived hormone-sensitive cancers and are of post-menopausal age have a significantly lower risk of breast cancer recurrence if they regularly eat lots of soy isoflavones, Chinese researchers reveal in an article published in CMAJ (Canadian Medical Association Journal). Isoflavones are produced virtually exclusively by members of the bean (Fabaceae/Leguminosae) family; they are a class of naturally occurring organic compounds, related to isoflavonoids. There has been a great deal of mention over the last few years regarding their cancer protecting qualities, especially prostate and breast cancers.
Soy isoflavones are phytoestrogens (dietary estrogens), they have a similar chemical structure to estrogen and can trigger estrogen-like actions in tissues, as well as inhibiting them. Because of their hormone-like actions, there has been concern regarding what impact they might have in hormone-sensitive cancers, such as estrogen and progesterone receptor positive breast cancers which depend on a good estrogen (or progesterone) supply to thrive.
Scientists from the Cancer Hospital of Harbin Medical University, Harbin, China monitored 524 patients who had undergone breast cancer surgery between August 2002 and July 2003 for 5 to 6 years. The authors explain that they aimed to find out what impact soy isoflavones might have on patients with breast cancer receiving adjuvant endocrine therapy (post-surgery hormone therapy).
They measured soy isoflavones dietary intake at baseline by giving the patients a validated food frequency questionnaire.
Dr. Qingyan Zhang and co-authors wrote:
Compared with postmenopausal patients in the lowest quartile of soy isoflavone intake (less than 15.2 mg/day), those in the highest quartile (more than 42.3 mg/day) had a significantly lower risk of recurrence.
The recurrence rate of estrogen- and progesterone- positive breast cancer was 12.9% lower among patients in the highest quartile of soy isoflavone intake than among those in the lowest quartile and was 18.7% lower for patients receiving anastrozole therapy in the highest quartile.
They add that the impact on overall survival was not significant in postmenopausal women, neither did they detect any improvement in premenopausal survival among women with high soy intake.
The researchers concluded:
High dietary intake of soy isoflavones was associated with lower risk of recurrence among postmenopausal patients with breast cancer positive for estrogen and progesterone receptor and those who were receiving anastrozole as endocrine therapy.
The majority of breast cancers are sensitive to estrogen, a female hormone. The sensitive cancer cells require estrogen for survival.
Removing estrogen from the patient’s body, or preventing any estrogen from getting into the cancer cells is an effective way of either destroying or controlling the cancer.
A chemical test on the tumor can determine whether it is hormone-sensitive. Tumors are usually classified as estrogen-sensitive or estrogen-insensitive.
Approximately half of all breast cancers that occur in premenopausal women and two-thirds among postmenopausal women are estrogen sensitive.
“Effect of soy isoflavones on breast cancer recurrence and death for patients receiving adjuvant endocrine therapy”
Xinmei Kang, Qingyuan Zhang, Shuhuai Wang, Xu Huang and Shi Jin
CMAJ 10.1503/cmaj.091298
Written by Christian Nordqvist