MADRID (Reuters) - Bristol-Myers Squibb’s immunotherapy drug Opdivo is a better and safer option than its older medicine Yervoy for treating melanoma patients who have had surgery to remove disease, researchers reported on Monday.

The finding represents an advance for so-called PDx drugs in treating cancer at an earlier stage, before it has spread around the body. At present, the use of such drugs, which help the immune system fight tumors, is confined to metastatic disease.

Doctors use surgery to remove melanomas when possible but such patients remain at high risk of relapse, creating a need for new treatment options.

So far Yervoy is the only drug approved in the post-surgery or adjuvant setting for this deadliest form of skin cancer, but the high doses of the medicine needed mean it can cause severe side effects and, as a result, use is limited.

Now results from a large clinical study presented at the European Society for Medical Oncology (ESMO) congress in Madrid show that 71 percent of patients given Opdivo for 12 months lived without disease recurrence against 61 percent for Yervoy.

The relapse-free survival rate for patients at 18 months was 66 percent against 53 percent.

Importantly, Opdivo - whose generic name is nivolumab -proved much better tolerated with only 14 percent of patients experiencing severe side effects against 45 percent of those on Yervoy.

The favorable balance of efficacy and safety means doctors are likely to opt for Opdivo instead of Yervoy, according to Jeffrey Weber of NYU School of Medicine, who was principal investigator on the study.

“In the future I think patients at significant risk of relapse will all be receiving nivolumab,” he said. “That will diminish the number of people that relapse and, at the end of the day, I would hope that it will prolong survival.”

The findings, which were also published online in the New England Journal of Medicine, underscore the progress scientists are making against melanoma.

Another study presented at the ESMO meeting showed a combination of two targeted drugs from Novartis also slashed the risk of melanoma returning after surgery. The Novartis treatment is designed for selected patients with a particular genetic mutation.