Now a study, published online in the New England Journal of Medicine, suggests that a drug that is used to treat melanoma can also help patients with MCC. The drug, called Keytruda or pembrolizumab, is approved to treat melanoma and lung cancer patients who no longer respond to other drugs.

It is hard to treat MCC when it reaches an advanced stage. Chemotherapy can shrink the tumor but patients often experience a recurrence quickly. What's worse, chemotherapy may affect the patients' immune system.

Keytruda blocks a pathway known as PD-1 and thereby enables the immune system to kill tumor cells. In new the study, the researchers tested the drug against MCC. The study included 26 patients with advanced MCC. The researchers treated them with Keytruda and evaluated 25 of them. They observed cancer shrink in 14 patients, four of whom no longer showed signs of the cancer. Furthermore, the cancer was under control in 12 of the 14 after six months.

Generally, the patients respond to chemotherapy for two to four months. It seemed that the new therapy could prolong patients' lives.

Previous research indicates that Merkel cell polyomavirus may be associated with MCC. Some evidence also shows that excessive ultraviolet exposure from the sun contributes to MCC.

In the latest study, 17 patients had tumors infected with the Merkel cell polyomavirus. The researchers found that the drug seemed to work regardless of the absence or presence of the virus. The drug led to side effects, such as fatigue. Two patients in the study had to stop taking the drug because it damaged their liver and heart muscle. However, both of them showed a response to the drug for a long period of time after stopping it.

The researchers wondered how long patients needed to stay on the drug. The findings of the study is encouraging, but more research is needed to test the drug.