Quercetin, when it is tested with melanoma tumor-cell cultures, the tumor cells die. This happens because the melanoma enzyme is tricked into stimulating so much quercetin that it changes and sensitizes the cancerous melanoma cells to the chemotherapy drug and dies. In this situation, quercetin is acting as a biological response modifier. A response modifier is a drug or a chemical compound acting to change the function of tumor cells to make them more responsive to chemotherapy or radiation.

A 2005 study published in the journal, Biochemical and Biophysical Research Communications, for instance, found that grape-derived resveratrol has an anti-proliferative effect on melanoma cancer cells -- anti-proliferative means that it blocks tumor cells from growing and spreading.