Researchers have identified a previously unknown virus and linked it to Merkel cell carcinoma, a rare but usually rapidly fatal skin cancer. The researchers, led by Drs. Yuan Chang and Patrick Moore of the University of Pittsburgh Cancer Institute, say it is too soon to know whether the virus causes the cancer, but their evidence suggests that it may be a contributing factor.

The virus, which they named Merkel cell polyomavirus (MCV), was reported in Science on January 17. It is related to a group of polyomaviruses, which has long been known to cause cancer in animals.

Merkel cell carcinoma has been linked to sun exposure and a weakened immune system, though its causes are not known. Approximately 1,500 cases are diagnosed in the U.S. each year. The incidence has been rising, particularly among individuals whose immune systems are compromised by AIDS or immunosuppressant drugs.

The researchers detected MCV DNA in 8 of 10 Merkel cell tumors they tested. By comparison, it was found in 5 of 59 (8 percent) control tissues from various body sites and 4 of 25 (16 percent) control skin tissues. It is not clear why most - but not all - Merkel cell tumors are infected with the virus.

Experiments indicated that the virus had infected human cells before the cells became malignant. In addition, the viral DNA was integrated in six of the eight tumors. This suggests that the virus plays a role in the tumor, the researchers note on a Web site describing the findings. They used a technique called digital transcriptome subtraction to isolate a viral DNA sequence that was similar to but distinct from all known viruses.

If MCV is shown to play a role in the cancer, investigators will have new leads to explore for understanding and treating the deadly disease. The discovery could have implications for other cancers, noted Dr. Kishor Bhatia of NCI's Center for Cancer Research.

In 1994, Drs. Moore and Chang discovered the virus that causes Kaposi sarcoma, the most common malignancy in AIDS patients and the most common cancer in Africa.