(Reuters) - Japan's health ministry has set a 50 percent cut in the price of Opdivo, a costly immune system-boosting cancer drug produced by Bristol Myers Squibb Co and marketed in the country by Ono Pharmaceutical Co Ltd, Ono Pharmaceutical said.

The halving of the price on Opdivo, approved in Japan for treating advanced melanoma, non-small cell lung cancer and kidney cancer, will take effect from February 1, 2017, Ono Pharmaceutical said in an emailed statement on Wednesday.

Japan's government-run health system typically adjusts drug prices every two years, but Opdivo's high price tag raised costs so much that officials decided to intervene with the steep price cut, according to local media reports and confirmed by Ono.

The company said the new Japanese price for a 20 mg vial of Opdivo will be 75,100 yen, and 364,925 yen for the 100 mg vial. Its current annual list price is 35 million yen ($321,787), based on the volume of drug needed to treat an average-size patient for a year.

Opdivo is part of a new class of cancer drugs designed to fight cancer by unleashing the body's own immune system to kill tumors.

In the United States, Opdivo's average list price is $13,100 per month, or $157,200 per year, according to Bristol Myers. The company said the U.S. price of Opdivo, first approved in late 2014, was increased by 1.5 percent earlier this year.

(Reporting By Deena Beasley in Los Angeles; Editing by Muralikumar Anantharaman)