A new study suggests that compounds found in black pepper and curry powder help halt the growth of stem cells that give rise to breast cancer.

Researchers at the University of Michigan Comprehensive Cancer Center applied piperine, found in black pepper, and curcumin, the main ingredient in the curry spice turmeric, to breast cancer cells in a laboratory dish. The spices, when used in combination, reduced the number of stem cells but did not harm normal breast cells.

The spice solution in this experiment was about 20 times more potent than the individual spices found in a typical diet. Because piperine and turmeric have not been tested in patients at risk for breast cancer, the study team does not encourage supplement use at this time. They plan to conduct a clinical trial to determine the safe dose of curcumin and piperine in people.

This year in the United States, doctors will diagnose 192,370 new cases of invasive breast cancer, according to the American Cancer Society.