Merkel cell carcinoma (MCC) is a rare type of skin cancer, affecting only a few thousand people each year, compared to tens of thousands with melanoma. But while it may not be as common as other skin cancers, MCC is highly aggressive and often deadly—and it’s also becoming more common, according to new research published in the Journal of the American Academy of Dermatology and presented at the American Academy of Dermatology 2018 Annual Meeting in San Diego.

“MCC is rare, but our research shows that it’s becoming less rare,” says board-certified dermatologist Paul Nghiem, MD, PhD, FAAD, head of the Division of Dermatology and George F. Odland Endowed Chair in Dermatology at the University of Washington in Seattle. “Compared to melanoma, MCC is much more likely to be fatal, so it’s important for people to be aware of it.”

Because melanoma incidence has been increasing over the last few decades, Dr. Nghiem and his colleagues suspected that MCC incidence was increasing as well. After examining data from the National Cancer Institute’s SEER-18 registry, they found that it was increasing even more than they had anticipated.

From 2000-2013, the number of reported MCC cases increased 95%, compared to 57% for melanoma and 15% for other cancerous tumors. Based on current population trends, Dr. Nghiem and his team predict that MCC incidence will grow from nearly 2,500 cases in 2013 to more than 3,200 in 2025.

Like other skin cancers, MCC is more likely to affect people with a prior history of skin cancer, men, Caucasians, and people older than 50. According to Dr. Nghiem, age is a particularly significant risk factor for MCC, with incidence rates increasing 10-fold between ages 40-44 and 60-64, and a further 10-fold between ages 60-64 and 85-plus.

“We believe the aging of the US population is likely driving the increase in MCC, as this cancer is much more prevalent in older individuals,” Dr. Nghiem says, adding that weakened immunity in this population may play a role in the disease.

MCC is associated with a virus, the Merkel cell polyomavirus, which is quite common, often found on normal human skin and surfaces that are frequently touched, Dr. Nghiem says. The vast majority of people don’t develop MCC after exposure to the virus, which is not associated with any other diseases, he says, but if someone’s immune system is not functioning well due to advanced age or other factors, that person may be more likely to develop MCC after encountering the virus.

MCC is also associated with unprotected exposure to ultraviolet light, a risk factor for all types of skin cancer. Because the disease is likely tied to cumulative exposure over time, Dr. Nghiem says, it’s important for everyone to protect themselves from the sun’s harmful UV rays. The AAD recommends a comprehensive sun protection plan that includes seeking shade, wearing protective clothing, and using a broad-spectrum, water-resistant sunscreen with an SPF of 30 or higher.

Like other skin cancers, MCC has the best prognosis when detected early. While the disease can be treated successfully in its early stages, Dr. Nghiem says, it is a highly aggressive cancer that is likely to grow quickly and metastasize. Although immunotherapy treatments that emerged in the last few years have vastly improved survival rates over previous chemotherapy treatments, metastatic MCC still has a high potential to be fatal, he says, making early detection especially vital.

According to Dr. Nghiem, MCC does not appear on the skin as a dark mole, like melanoma. Instead, it appears as a firm lump that is red, purple, or skin-colored. Some people may mistake MCC for a cyst or folliculitis, he says, but MCC lesions are typically not tender like the bumps caused by these other conditions. Additionally, he says, MCC tends to grow rapidly.

“If you notice a new, unusual growth, especially one that looks different from the other spots on your skin or one that is growing quickly, see a board-certified dermatologist for diagnosis,” Dr. Nghiem says. “If you do have MCC, it’s important to receive care from a qualified team of physicians that understands how to manage this disease, and your dermatologist can help ensure you get the care you need.”