The U.S. Food and Drug Administration (FDA) approved Merck & Co.'s advanced treatment for melanoma called Keytruda.

The federal agency released a statement that Keytruda is ready to be used as a treatment for melanoma. This medicine is one of the first to use a protein called PD-1, which boosts the patient's immune system so that it can fight the cancer cells. Aside from Merck & Co., other companies, such as Novartis AG (NOVN) and Bristol-Myers Squibb Co., are developing drugs using the same protein.

According to the U.S. Centers for Disease Control and Prevention, skin cancer is the most common type of cancer in the United States. Most of the cases are melanoma, the deadliest kind of skin cancer, which is often caused by overexposure to ultraviolet light. In 2011, 70,853 people were diagnosed with the disease with a 17 percent mortality rate.

The drug was approved two months earlier than expected through the agency's accelerated approval program that allows manufacturers to market the drugs after showing positive results in the clinical trials, Bloomberg reported.

However, Merck is still required to provide evidence that the drug improved the user's overall health and survival rate.

Keytruda is recommended to those who have previously taken Yervoy, an immunotherapy drug developed by Bristol-Myers. Those who tested positive for a gene mutation called BRAF must first undergo a therapy that will block the production of such gene before using the melanoma drug.

The price of the drug is pegged at $12,500 per month or around $150,000 per year. Keytruda is administered every three weeks. Analysts predicted that it could generate revenue of more than $6 billion.

"PD-1 is truly a game-changer. It's active in a way that other drugs are not," Lynn Schuchter, a medical oncologist at the Abramson Cancer Center of the University of Pennsylvania and one of the researchers involved in the clinical trials of the melanoma drug, told the Wall Street Journal. "And what's been interesting is the activity of PD-1 beyond melanoma. It looks to be active in bladder and renal and lung cancer. So this is bigger than melanoma."