Study: Soy Protein Found to Speed Up Growth of Breast Cancer

08 Sep 2014 --- Soy may accelerate the rate that breast cancer spreads, according to the latest research. A study, published in the September issue of the Journal of National Cancer Institute, has found that high levels of soy protein genistein could speed up the progression of breast cancer cells.

Previously there has been a belief that soyfood intake could be linked with a reduced cancer risk. More recently though scientists have stated that soy is a food that does not actually help cancer patients, and may actually increase the rate of tumour growth. 

For this recent study, researchers at the Memorial Sloan Kettering Cancer Centre in New York studied 140 women diagnosed with invasive breast cancer. All of the women in the study had recently had breast biopsies and were diagnosed with stage one or two cancer. All were scheduled to have a mastectomy or lumpectomy within two to three weeks of the date the study took place.

Before they underwent surgery to remove their cancer, half of these women took soy protein powder containing genistein, while the other 50% took a placebo. 

Tumour tissue was compared from before and after the operation, and scientists then found evidence of genes which are known to promote cell growth, from tissue taken from some of the women who had taken the soy supplement. 

The changes were seen in women who consumed around 51.6g of soy, which is the equivalent of four cups of soy milk a day. 

The study did not identify any links to soy in terms of its ability to prevent breast cancer or whether it could have any effect on women who had not already been diagnosed with the disease. 

The researchers did warn that those living in Asian countries (and already suffering from breast cancer) could be especially at risk, due to the high levels of tofu and soy in their traditional diets. 

Discussing the genes which were found in the women who had taken the soy supplement, Jacqueline Bromberg, co-author of the study, is reported to have said, “It is not clear that this will translate into actual tumour growth, but the concern is that there may be the potential.

'If you currently have early-stage breast cancer, don't eat soy in large amounts,” she said. “If you've had breast cancer, you can eat soy but in moderation.”

Links between soy and breast cancer have been discussed in previous studies, and the food has often been considered to be a useful addition to the diet in the prevention of breast cancer. In 2002, a study questioned the association between soyfood intake and breast cancer risk in Asian-Americans. It concluded that high soy intake in childhood in Asian-Americans is associated with reduced breast cancer risk, and this risk could be further reduced by intake as an adult. 

But the researchers from this more recent study have said that more work needs to be done before any recommendations about soy can be made. They stressed also that the impact of soy on breast cancer is still not yet fully understood.