A drug used to fight off parasites may someday be used to protect against skin cancer, according to new research.

Doctors have used the drug, DFMO, for years to treat African sleeping sickness caused by parasites. Researchers, however, noticed, that years after taking the drug, patients had a decreased chance of getting nonmelanoma skin cancers.

The results, as yet unpublished in a peer-reviewed paper, were presented during the International Conference on Frontiers in Cancer Prevention Research conference that ends Tuesday.

Drugs sometimes have unexpected side effects that companies capitalize upon. The most famous example is the class of drugs now known for treating impotence that was originally used for heart problems.

Howard H. Bailey, professor of medicine, and study presenter Sarah Lamont, a medical student, both from the University of Wisconsin School of Medicine and Public Health presented the research.

The two followed 209 people with a history of nonmelanoma skin cancer who had taken DFMO, part of a randomized, double-blind study. The people were either given DFMO or a placebo for four to five years.

We found there is still evidence that the men and women assigned to DFMO for five years continued to have a lower incidence of nonmelanoma skin cancers compared with people assigned to placebo, Bailey said. What we saw was that the presumed benefit that people got in taking DFMO appeared to persist for years after stopping it.

Combing through the participants' medical records comes with limitations, the researchers admit.

Participants may have been followed differently or changed their behaviors to limit sun exposure because of being in the original study, Bailey said.

Our data suggest that the protective event that we saw in our prospective study appears to continue and there was no evidence of any rebound effect, he said. We did not find any evidence that the people who received DFMO were harmed.

However, Bailey cautioned, more studies are needed before DFMO can be recommended as a prophylaxis against nonmelanoma skin cancers.

He added that such prophylaxis measures are needed because public health efforts to teach people about limiting sun exposure have not resulted in fewer cases of skin cancer, with more than 2 million cases of nonmelanoma skin cancer diagnosed each year. The incidence continues to rise despite public health efforts to get people to lessen their sun exposure, Bailey said.