New findings suggest black cohosh increases spread of breast cancer

A new study on mice suggests that the herb black cohosh, used by women as an alternative to HRT to treat menopause symptoms, may speed up the spread of tumors in women with breast cancer.

Researchers at the Mylan School of Pharmacy at Duquesne University in Pittsburgh say that their findings show the natural menopause treatment could be unsafe for women who do not know that they have breast cancer.

"Although it is unfortunate to be eliminating another option for women needing therapies to relieve menopausal symptoms, our findings suggest that women who may be at high risk of having an undetected breast tumor and certainly those who do have breast cancer should proceed with great caution - or simply avoid - taking black cohosh until we learn if there are ways to circumvent these adverse effects,"​ said Dr Vicki Davis, lead researcher and assistant professor at the Mylan School of Pharmacy and Graduate School of Pharmaceutical Sciences at Duquesne University​, speaking at an American Association for Cancer Research meeting held in Washington on Saturday.

The Duquesne team used two groups of sexually mature female mice. All mice had been bred to spontaneously develop mammary tumors through the activation of an oncogene common in human breast cancer. These tumors spread in time to other parts of the body, as occurs with invasive breast cancer. One mice group was fed a black cohosh dose comparable to women ingesting 40 mg/day (the amount of a standardized herbal supplement normally recommended for menopausal symptoms) for 12 months.

In the black cohosh-treated mice, the incidence of new tumors did not increase, suggesting that black cohosh will not increase or decrease a woman's risk of developing breast cancer. However, in the mice that developed mammary tumors, there was an increase in the number of tumors that spread to the lung - 27.1 per cent of treated mice compared to 10.9 per cent of the mice on the control diet. The increase in the number of lung tumors in each female after long-term exposure to black cohosh suggests that this herbal therapy may increase the aggressiveness of the mammary cancer, said the researchers, who were fundedby the Susan G. Komen Foundation.

The data presented suggest that the recommended doses of black cohosh may promote progression to metastatic disease in women with early stage breast cancer, concluded Dr Davis.

Hormone replacement therapy has been found to worsen the risk of heart disease, stroke and some cancers, fuelling the search for a natural alternative to reduce the hot flashes and other symptoms experienced by menopausal women.

Much of the evidence so far finds black cohosh and other herbs used for this purpose, such as red clover, to be safe. The controversy is usually over the effectiveness of these herbs, with a recent study out last week concluding that red clover was no more effective than placebo at relieving hot flashes.At the same time, numerous other trials find these two herbs to be both safe and effective.

While the Duquesne researchers could not explain how black cohosh may make cancer more likely to spread, both the natural health and conventional health industry will welcome further trials, such as the one announced recently at the University of Chicago, Illinois, to investigate herbal remedies for menopausal women.

For proceedings of last weekend's meeting, see the AACR website​.