A combination of two topical drugs that have been in use for years triggers a robust immune response against precancerous skin lesions, according to a new study. The research, from Washington University School of Medicine in St. Louis and Harvard Medical School, shows that the therapy activates the immune system’s T cells, which then attack the abnormal skin cells.

The study, which involved patients with actinic keratosis, a precursor to a type of skin cancer called squamous cell carcinoma, is published Nov. 21 in The Journal of Clinical Investigation.

“We looked at precancerous lesions on patients with sun-damaged skin,” said Washington University dermatologist and study co-author Lynn A. Cornelius, MD, director of the Division of Dermatology. “Most commonly found on the face, scalp and arms, these lesions appear abnormal by visual examination and under the microscope but are not full-blown skin cancers. But because these lesions have the potential to develop into a true skin cancer, they are commonly treated. Our study shows this combination therapy is more effective and better tolerated than current treatment practices.”