Merck & Co., the world's fourth-biggest pharma company by revenue, has reported positive results from tests of its new drug Keytruda (pembrolizumab) against 30 cancer types.

Tests have shown Keytruda is effective against triple negative breast cancer, melanoma, non-small cell lung cancer, stomach cancer, head and neck cancer, bladder cancer and Hodgkin's lymphoma, among others.

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"We've now shown efficacy against seven cancers," said Dr. Alise Reicin, Merck's vice president for cancer drug development.

The patients received infusions of Keytruda every two weeks and periodic scans to determine the drug's effects. The study showed 33 percent of patients had some tumor shrinkage while 19 percent had tumors shrink at least 30 percent.

Triple-negative breast cancer, which affects 15 percent to 20 percent of 1.7 million new breast cancer patients every year worldwide, doesn't respond to three of the main types of treatment. These three target the hormones estrogen and progesterone and a protein called HER-2 that fuel cancer growth.

Merck said Keytruda shrank tumors to some extent in one-third of 27 patients in a study called Keynote-012. All had triple-negative breast cancer that spread outside the breast.

Keytruda  belongs to a new class of medicines, mostly experimental, called immuno-oncology drugs.

They fight cancer through a mechanism that "uncloaks" a substance called PD-1 on hidden cancer cells so they can be attacked by immune cells called T cells.

Merck said it will start mid-stage patient tests of Keytruda in the first half of 2015. It's received accelerated approval for advanced melanoma.

Melanoma is the most dangerous kind of skin cancer. 

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