Epidemiological studies suggest soy supplementation can benefit breast cancer sufferers but there is conflicting evidence concerning its efficacy, the researchers wrote in the Journal of the National Cancer Institute.
Soy can exhibit either pro- or anti-estrogenic effects and may affect other cellular events, so it could be both protective and harmful, explained lead scientist Dr Moshe Shike.
“Soybeans contain the isoflavones genistein and daidzein. Genistein stimulates growth of estrogen-sensitive breast cancer (BC) cells and can block the inhibitory effects of tamoxifen. However, isoflavones have also been reported to decrease BC cell growth,” he said.
Two-fold increase in genes
In the randomised placebo-controlled study, Dr Shike and his team in New York analysed the effects of soy supplementation on gene development and markers of breast cancer risk among women diagnosed with invasive breast cancer (adenocarcinoma).
When tumour tissue from the diagnostic biopsy and post-treatment surgery was examined the researchers observed changes in several genes that promote cell cycle progression and proliferation among women in the soy group.
A two-fold increase in gene expression was observed in some cases, including the FGFR2 gene known to induce cancer growth. This was possibly linked to raised levels of genistein.
“A high-genistein signature consisting of 126 differentially expressed genes was identified from microarray analysis of tumours. This signature was characterised by over-expression of cell cycle transcripts, including those that promote cell proliferation.”
In one sample gene expression increased from already elevated pre-treatment levels, which suggested the initial molecular alteration was reinforced by soy.
"These data raise concern that soy may exert a stimulating effect on breast cancer in a subset of women."
The four-year study (from 2003 to 2007) involved 140 patients scheduled for resection (surgery) who were randomly chosen for either soy supplementation (soy protein) or placebo (milk protein).
Patients were instructed to take two 25.8g packets of supplementation per day mixed with water or juice from the day of consent to the day of surgery.
To see the soy sector response to this research click here.
Source: Journal of the National Cancer Institute
‘The effects of soy supplementation on gene expression in breast cancer: a randomized placebo-controlled study’
Authors: Moshe Shike, Ashley S.Doane, Lianne Russo, Rafael Cabal, Jorge, Reis-Filo, William Gerald, Hiram Cody, Raya Khanin, Jacqueline Bromberg, Larry Norton