Jennifer Matthews: Mary Louise Gramkow spent her life in the sun.Mary Louise Gramkow: Tennis, gardening and mowing. That sort of thing. Just an outdoor person.Jennifer Matthews: All that sun damaged her legs -- causing a skin condition called actinic keratoses. These thick and crusty lesions are a precursor to skin cancer.Dr. Lisa Kauffman: This is an actinic keratosis that eventually transformed into a squamous cell skin cancer.Jennifer Matthews: Today, she's having the rest of the spots treated -- hoping to prevent more cancer. Doctor Kauffman applies levulinic acid to the lesions to make them sensitive to light. Around 18 hours later, she returns for the second treatment.This blue light activates the acid and destroys the lesions.Dr. Lisa Kauffman: So, this treats at least 85 percent of the pre-cancerous growths that are here today.Jennifer Matthews: In studies, all patients had more than 85 percent of their lesions clear. But it's not a cure. Sun exposure will mean more lesions and more needed treatment. Mary Louise had her left leg done a few months ago.Mary Louise Gramkow: My left leg is very much better, but there are a couple of places that, as Dr. Kauffman said, I think were too thick and they have to be done again.Jennifer Matthews: Mary Louise says it's uncomfortable, but a treatment she's willing to endure again if necessary. This is Jennifer Matthews reporting.