When breast cancer patients and their doctors discuss chemotherapy, they need to talk about complementary and alternative medicines like supplements and herbs, researchers warn.

The use of such medicines has increased among women with breast cancer over the past two decades, but a new study published in JAMA Oncology found that breast cancer patients who use a lot of these unconventional therapies are more likely to skip recommended chemotherapies.

"From a public health perspective, there really needs to be a discussion between patients and providers about whether women are using (complementary and alternative medicine) therapies, why are they using them and are their goals realistic," said lead author Heather Greenlee of the Mailman School of Public Health at Columbia University in New York.

Greenlee and colleagues studied 685 U.S. women with invasive breast cancer that had not spread. The women were under age 70 and had enrolled in the study between 2006 and 2010.

When they first joined the study, 87 percent of the women reported using vitamins and/or minerals, herbs and/or botanicals, other natural products, mind-body self practice or mind-body practitioner-based practice.

About 45 percent of the women should have received chemotherapy based on National Comprehensive Cancer Network guidelines. The other women fell into a discretionary category where the decision to undergo chemotherapy is based on a discussion with their doctors.

Overall, 89 percent of the women who should have received chemotherapy did so within 12 months of starting the study. About 36 percent of those in the discretionary group also chose to undergo chemotherapy.

In the discretionary group, use of complementary and alternative medicine was not tied to women's decisions about chemotherapy.

But in the group for which there was evidence to support a benefit of chemotherapy, women who were using supplements or a lot of complementary and alternative medicines were about 84 percent less likely to have received chemotherapy compared to women who didn't use those alternative approaches.

When the researchers looked at individual types of complementary and alternative therapies, they found mind-body practices weren't tied to the decision to undergo chemotherapy.

Greenlee and her colleagues can't say why women who used supplements or a lot of complementary and alternative methods were less likely to undergo guideline-supported chemotherapy. It could be that women were choosing these other methods as alternatives to chemotherapy.

"The good news is that 89 percent of the women who were clinically indicated to receive chemotherapy, received chemotherapy," Greenlee told Reuters Health.

In a commentary accompanying the new study, Robert Zachariae of Aarhus University Hospital in Denmark writes that doctors who treat cancer need to discuss use of complementary and alternative therapies with their patients.

Only by acknowledging that complementary and alternative medicines are important to cancer care will oncologists be able to help patients to make sufficiently informed choices, Zachariae writes.