– Merkel cell carcinoma, an extremely rare form of skin cancer, is often caused by a subclinical virus that routinely inhabits the skin. Now, a serum test of virus antibody levels is offering insight into the state of the disease, according to one dermatologist.

“If you have these antibodies, you have a better prognosis. You can follow those antibodies to test for recurrence or progression,” Isaac Brownell, MD, PhD, of the Dermatology Branch of the National Institutes of Health said at Skin Disease Education Foundation’s annual Las Vegas Dermatology Seminar.

The cancer appears in the skin’s Merkel cells, which contribute to our sense of touch by helping us to discriminate textures. “When you put your hand in your pocket, and you can tell the difference between the front and back of a quarter,” he said, “you’re using the Merkel cells in your fingertips.”

Only about 2,500 cases of Merkel cell carcinoma appear in the United States each year, Dr. Brownell said. It appears more often in elderly white patients, is more common in men than women, and is more likely among immunosuppressed patients, whose risk is increased 15- to 20-fold. Cases are more common in sunnier regions – at least in men – and lesions frequently appear on the head, face, and neck.

Five-year survival is estimated at 51% if the cancer is localized, according to a 2016 study of 9,387 cases that Dr. Brownell highlighted. But survival declines dramatically if it has spread to lymph nodes or distant sites (Ann Surg Oncol. 2016 Oct;23[11]:3564-71).

In recent years, researchers have linked 80% of Merkel cell carcinoma cases to the Merkel cell polyomavirus, he said. The virus normally inhabits our skin with no ill effects, he said. “We all have this virus on our skin. It’s everywhere, and even children have antibodies,” he said. But mutations can lead to Merkel cell carcinoma.

Does it matter if cases are polyomavirus positive or polyomavirus negative? Not really, Dr. Brownell said, since the presence of the virus doesn’t appear to affect overall prognosis. However, he said, serum antibody testing can be helpful in polyomavirus-positive patients because it offers insight into prognosis and tumor burden. For example, “if the baseline titer falls and then starts to go up, they’re likely to have a recurrence, and you’ll want to look out for that,” he said.

Dr. Brownell offered another bit of advice: Be prepared to respond to patients who worry that they have a contagious virus and could be a danger to others. The proper answer, he said, is this: “You don’t have to worry about infecting people. Your tumor is not making the virus, you’re not infectious, and we have the virus on us already.”

For more information about the antibody test, visit merkelcell.org/sero.

Dr. Brownell reported having no relevant disclosures. SDEF and this news organization are owned by the same parent company.