The US Food and Drug administration (US FDA) has approved Merck's Keytruda, used for patients with advanced melanoma. It belongs to a new class of cancer drugs that help unleash the body's immune system to fight tumors.

Keytruda is the first drug, which has been approved, that inhibits the action of protein PD-1, or programmed death receptor 1.

"This is really opening up a whole new avenue of effective therapies, previously not available. It allows us to see a time when we can treat many dreaded cancers without resorting to cytotoxic chemotherapy,"said Dr Louis M Weiner, director, Georgetown Lombardi Comprehensive cancer center, and a spokesman for the American Association for cancer research.

The cost of treatment using this drug would be about $12,500 a month.

Since the preliminary trials of the drug showed positive results, it was given accelerated approval by the FDA, allowing it to reach the market without going through the three typical phases of clinical trials needed to show that a drug can prolong lives. However, the company has to conduct two controlled clinical trials to verify that the drug can delay the progression of disease and extend life expectancy.