They said curcumin, found in the spice turmeric, interferes with melanoma cells.
Tests in laboratory dishes show that curcumin made melanoma skin cancer cells more likely to self-destruct in a process known as apoptosis.
The same team has found that curcumin helped stop the spread of breast cancer tumour cells to the lungs of mice.
Bharat Aggarwal and colleagues of the Department of Experimental Therapeutics at the University of Texas MD Anderson Cancer Centre in Houston treated three batches of melanoma cells, known as cell lines, with curcumin at different doses and for varying times.
The curcumin suppressed two proteins that tumour cells use to keep themselves immortal, the researchers write in next month's issue of the journal Cancer.
"Based on our studies, we conclude the curcumin is a potent suppressor of cell viability and inducer of apoptosis in melanoma cell lines," Aggarwal's team wrote.
"Future investigation to determine the effects of curcumin in animal models of melanoma and clinical trials are planned."
Earlier research has shown that curcumin, which acts as an antioxidant, can help prevent tumours from forming in the laboratory.
Aggarwal said people who eat plenty of turmeric have lower rates of some cancers, although the spice itself has not been shown to reduce cancer risk in people.