Lawyers evaluating claims that Viagra caused men to develop deadly melanoma skin cancer say a recent large-scale study of more than 25,000 patients will carry a great deal of weight in Viagra lawsuits, according to the New Jersey Law Journal.

But in order to solidify the nexus between the popular erectile dysfunction drug and the deadly skin cancer, researchers must work to evaluate the cause and effect, Kelly Jones, a member of a New Jersey Drug and Medical Device Steering Committee, told the publication.

“It is important to keep in mind that a correlation or association is not equal to causation, and early signals in research must be followed up by well-controlled epidemiological studies,” said Jones.

A study published in the peer-reviewed medical journal JAMA Internal Medicine showed a possible link between Viagra use and an increased risk of developing melanoma. The study found that Viagra users were 84 percent more likely to develop melanoma than those who did not use the erectile dysfunction drug.

The study looked at men who participated in an earlier Health Professionals Follow-up Study, a Harvard University project that began in 1986. After adjusting risk factors, men who had used Viagra (sildenafil) had nearly twice the risk of developing melanoma skin cancer, though there was no risk increase noted for other skin cancers such as basal cell and squamous cell carcinoma.

Every two years the men who participated in the study filled out health and lifestyle questionnaires. In 2000, the questionnaire began asking about the use of erectile dysfunction drugs. That year, 1,618 men reported having ever used Viagra.

“Over the next decade, among the 29,929 men who said they had never used Viagra, 128 developed melanoma,” the report said. “Among the 1,618 Viagra users, 14 developed melanoma. In other words, 4.3 of every 1,000 who didn’t take Viagra developed melanoma compared to 8.6 of every 1,000 men who took Viagra.”

Philadelphia lawyer Thomas Kline told the New Jersey Law Journal that he believes that Viagra melanoma lawsuits will have much better results for plaintiffs than those that came on the heels of a 2006 study that Viagra users with a history of heart problems had an increased risk of blindness.

“We believe this is different,” Kline said. “We believe this is a very large-scale study which shows there is a significant association between the drug and melanoma.”

Additionally, he said, the authors’ affiliation with Harvard and other top universities makes it an “impressive and significant and very important piece of medical information.”

The federal judge assigned in the multidistrict litigation in the blindness lawsuits dismissed the cases after finding that an expert report by the study’s author contained numerous errors.

U.S. District Court Judge Paul Magnuson said he had “serious concerns” about the report’s reliability, which found that Viagra users with a history of heart attacks had a statistically significant increased risk of suffering an eye condition that can result in partial or total blindness. The study was small – 76 men – and included some people who didn’t begin taking Viagra until after developing vision problems.