Soy and Recurrence Risk
This is one of those studies that seems to confound everything we have known. The standard and long-standing advice for women with breast cancer, especially those with ER positive breast cancers, has been to avoid soy. It has always been fine to occasionally have tofu, but the recommendation has been pretty firm re soy supplements, soy milk on your daily cereal, etc. Now here comes a study that suggests that the intake of soy may lower the risk of recurrence for exactly these same women. My own strong suggestion would be to remember that this is a single study, and that it would be wise to speak with your doctor before making a real change in your diet.
Soy isoflavones may reduce breast cancer recurrence risk in some patients
By Laura Dean
19 October 2010
CMAJ 2010; Advance online publication
MedWire News: A high dietary intake of soy isoflavones is associated with a reduced risk for breast cancer recurrence among postmenopausal women with hormone receptor-positive disease treated with anastrozole, Chinese researchers report.
The same association was not observed among premenopausal women, note Xinmei Kang and colleagues from Harbin Medical University.
Soy isoflavones - found in soybeans and soy products - have weak estrogenic effects, which has led to concerns about the consumption of these products by patients with hormone-sensitive breast cancer, say the researchers.
To investigate whether soy isoflavones influence breast cancer recurrence and death, Kang and team measured the dietary intake of soy products among 524 patients who were receiving adjuvant endocrine therapy after breast cancer surgery.
Of the patients, 248 (47.3%) were premenopausal and 276 (52.7%) were postmenopausal. All patients had cancer that was positive for estrogen receptor (ER), progesterone receptor (PR), or both.
During a median follow-up of 5.1 years, there were 185 (35.3%) recurrences and 154 (29.4%) deaths.
The researchers report that, among the postmenopausal women, soy isoflavone intake was inversely associated with breast cancer recurrence. Specifically, women in the highest quartile of intake (>42.3 mg/day) had a 33% reduced risk for recurrence compared with those in the lowest quartile of intake (<15.2 mg/day).
Further stratification of the patients by hormone receptor status and type of adjuvant therapy (tamoxifen or anastrozole) revealed that the observed association was restricted to patients with breast cancers positive for both ER and PR, and those treated with anastrozole.
In contrast, there was no association between intake of soy isoflavones and breast cancer recurrence among premenopausal patients, and there was no association between soy isoflavone intake and death in either group of patients.
Writing in the Canadian Medical Association Journal, Kang and co-authors suggest that soy isoflavones exert their protective effect by inhibiting the local production of estrogens from circulating precursors in breast tissue. They conclude that while their findings are potentially important in terms of recommendations for intake of soy isoflavones in conjunction with endocrine therapy, large multicentre clinical trials are needed to provide more data.
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