"The results of this study show that the topical application of this drug, even after sun exposure, can prevent skin cancer in these patients," says Daniel Yarosh, PhD, lead author of the study and head of Applied Genetics Incorporated Dermatics, the New York-based company thatis developing the lotion.

A skin cancer expert affiliated with the American Cancer Society (ACS) calls the study well-done, and its results exciting.

"It was a rigorous study that showed this treatment reduced the frequency of skin cancers among these patients," says Martin Weinstock, MD, PhD, professor of dermatology atBrown University, and chair of the ACS Skin Cancer Advisory Group. "This is the first time something like this has ever been demonstrated."

"And up until now our main hope for preventing skin cancer has been before the damage is done, with sun screens and sun protection, which are not always well used," Weinstock notes. "This is exciting because it gives the possibility of preventing skin cancer after sun exposure," he adds.

"However, there are still a lot of questions to be answered," adds Weinstock. "XP patients are known to have this gene defect; we don?t know yet whether it would work in the general population who don?t have XP; it will take more research to learn that."

Skin cancer usually begins when sunlight damages skin cells? DNA. If a cell cannot repair its damaged DNA, when it divides it may produce new cells with a weakened ability to control their growth and replication. Uncontrolled growth of such abnormal cells is cancer.

A cell?s genes normally produce enzymes that repair any DNA damage so that a cell does not become cancerous. But patients with XP have inherited a mutated gene that cannot produce the repair enzyme. That makes XP patients up to 1,000 times more likely to develop skin cancer than the general public, and 50% develop a skin cancer by age 8. XP patients often have so many skin cancers that they can become disfigured from the surgeries needed to remove them.

The researchers found a bacterium whose genes produce a DNA repair enzyme and tests showed it worked in human cells in lab dishes. The researchers enclosed the enzyme in an oil-based membrane attractive to human skin cells, which surround and ingest it. Once inside the cell, the membrane dissolves, releasing the enzyme to do its repair work.

In the year-long study, 20 patients with XP applied the lotion to sun-exposed areas on a regular basis after sun exposure, while 10 used no lotion. Patients using the lotion developed about 28% fewer new basal cell skin cancers and about 66% fewer occurrences of a pre-cancerous condition called actinic keratosis, which can lead to squamous cell skin cancer.

The researchers plan a 600-person study to see if the lotion will reduce the chance of developing skin cancer in people who don?t have XP, but who are at increased risk of developing skin cancer due to previousskin cancers. The ultimate goal, say the researchers, is a skin cancer preventative for the general population.

• Can Skin Cancer Be Prevented?
• What are Clinical Trials?
• National Cancer Institute (NCI) (1-800-4-CANCER)