Merck trial shows more melanoma cancer patients respond to drug Mon Nov 18, 2013 12:05pm EST (Reuters) - Early data from a small trial of Merck & Co Inc's experimental immunotherapy cancer drug, known as MK-3475, show that about half of advanced melanoma patients treated with the highest dose of the drug experienced tumor shrinkage. Updated results from the early-stage trial are set to be presented on Monday at the International Congress of the Society for Melanoma Research in Philadelphia. The antibody drug is part of a new class of compounds designed to block the activity of a receptor on immune cells called programmed death 1, or PD-1. The aim of the drugs is to spur the body's own immune system to attack cancer cells. Merck said results from 135 patients whose melanoma had stopped responding to earlier rounds of treatment showed that 41 percent had tumor shrinkage - the rate was 51 percent in the high-dose group, and 40 percent for lowest-dose group. The company estimated overall survival at a year of treatment at 81 percent, but said the trial had not yet reached either a median duration of response or median overall survival. Serious side effects seen in the trial included fatigue, rash, increased liver enzymes and renal failure. Reporting By Deena Beasley; Editing by Bernard Orr