A bee sting can be painful, but its venomous payload might hold promise for a beneficial purpose—fighting cancer.

Researchers at Washington University in St. Louis have used an ingredient of bee venom called melittin to shrink or slow the growth of tumors in mice. Melittin's anti-tumor potential has been known for years, but it hasn't been used as a drug because it also attacks healthy cells, including vital red blood cells.

Now...