Thursday’s order by the U.S. Judicial Panel on Multidistrict Litigation coordinated the cases, now totaling more than 100, for pretrial purposes to U.S. District Judge Richard Seeborg. The suits, most of which were filed this week in the Northern District of California, have been brought by men diagnosed with melanoma or by the estates of those who died from the deadly form of cancer.

They cite studies finding that the enzyme used in Viagra, which the U.S. Food and Drug Administration approved in 1998 for the treatment of erectile dysfunction, causes a cell mutation that could develop into melanoma. In particular, a 2014 study in the Journal of the American Medical Association Internal Medicine found that men who took sildenafil, the active ingredient in Viagra, had an increased risk of developing melanoma by up to 84 percent.

According to the suits, Viagra has been prescribed to more than 35 million men.

Seeborg, the only judge recommended by plaintiffs attorneys before the MDL panel, already was overseeing most of the Viagra suits. Ernest Cory, co-founder of Cory Watson in Birmingham, who has filed many of the lawsuits, moved on Dec. 11 to coordinate the cases. Many of the suits have been filed by other firms including Minneapolis-based Robins Kaplan and Motley Rice of Mount Pleasant, South Carolina.

In an emailed statement, Pfizer spokeswoman Neha Wadhwa wrote: “Viagra’s safety and efficacy have been studied in 136 clinical trials, and there is no reliable scientific evidence that the medicine causes melanoma. Pfizer stands behind this important medicine and intends to vigorously defend these lawsuits.”

Pfizer attorney John Joiner, a partner at Washington’s Williams & Connolly, had supported transfer of the cases to Seeborg but denied the allegations, claiming the 2014 study had “significant limitations.”