WHITEHOUSE STATION, N.J. (AP) — U.S. regulators have approved the first drug in a new class of cancer medicines that work by stimulating the immune system, a Merck drug developed for treating deadly skin cancer.

The Food and Drug Administration says it has granted accelerated approval to Merck's Keytruda (Key'troo-dah), for treating melanoma that's spread or can't be surgically removed, in patients previously treated with another drug.

The drug, known chemically as pembrolizumab (pem-BROH'lizz-you-mab), is part of a hot, promising new class of antibody-based drugs that work by taking a brake off the immune system so it can better recognize and attack cancer cells.

Merck's drug is the first in the class approved in the U.S. Rival Bristol-Myers Squibb and a partner got a similar drug approved in Japan in July and are seeking U.S. approval.