Although Merkel cell carcinoma can develop undetected or at a metastasized site, it usually first appears as a painless lump or nodule on an area of the skin that has been exposed to the sun.
Merkel cell carcinoma is a rare form of malignant skin cancer that has historically appeared mainly in the elderly and people who have compromised immune systems, but new research suggests this disease is becoming increasingly common.
Although Merkel cell carcinoma can develop undetected or at a metastasized site, it usually first appears as a painless lump or nodule on an area of the skin that has been exposed to the sun. These cancerous areas don’t usually appear on mucosal tissues, as ulcers, or as multiples. Instead, these singular lumps can be red to violet, smooth and shiny, measuring about 1 centimeter to 2 centimeters, and appear mostly on the head and neck. The appearance of Merkel cell carcinoma on the limbs is possible, too, but its appearance in certain areas varies by demographic. For example, Merkel cell carcinoma appears on the legs more in women, and anogenital lesions develop almost exclusively in black patients.
Overall, Merkel cell carcinoma is more common in men, older adults, and in people who are immunocompromised, according to a 2022 paper published in Dermatologic Therapy. Incidence rates are more than double in men, according to the report, with an incidence of about 1.9 per 100,000 in women compared to 4.2 per 100,000 in men.
Increasing age is another risk factor, with most cases of Merkel cell carcinoma diagnosed in the mid-70s. The risk of developing this condition increases by about 10-fold every 20 years, researchers note.
Another major risk factor is immunosuppression, especially after solid organ transplantation. People who have undergone these types of transplants are about 24-times more likely to develop Merkel cell carcinoma than the general population, with the greatest risk occurring about a decade after transplantation.
Merkel cell carcinoma may initially be misdiagnosed as a simple cyst or benign lump because of its asymptomatic appearance, but a more specific diagnosis can be made with a skin biopsy, the study reveals. According to researchers, a biopsy that is positive for Merkel cell carcinoma may feature things like:
Suspicion of Merkel cell carcinoma should be followed with a full skin and lymph node examination, as well as a general history and physical examination.
Outside of the risk factors already mentioned, there are two reasons Merkel cell carcinoma usually forms—as a result of DNA damage from ultraviolet light or from infection with a DNA virus from the Polyomavirus family.
There are some characteristics that can be protective against Merkel cell carcinoma, though—particularly skin pigmentation. About 95% of cases of Merkel cell carcinoma diagnosed between 1973 and 2006 were in white patients, the study notes, with the lowest risks in black, Hispanic, and Asian populations.
Surgical removal or resection is the most common way to remove primary Merkel cell carcinoma tumors, although several new medications have been introduced in recent years that offer systemic treatment options in the event of metastasis. Radiation, chemotherapy, and T-cell inhibitors have all shown s0ome degree of success in treating Merkel cell carcinoma. Roughly half or more of patients treated with targeted therapies like T-cell inhibitors respond to these treatments, although more advanced stages of Merkel cell carcinoma are notoriously difficult to treat and largely unresponsive to existing treatment options.
Loren E. Hernandez, a research fellow at the University of Miami Miller School of Medicine and lead author of the 2022 study says continued investigation into the diagnosis and treatment of Merkel cell carcinoma is important considering the observed increase in cases.
According to the study, cases of Merkel cell carcinoma have increased by about 95% since 2000, and more than 3,000 new cases per year are expected to be identified by 2025.
“Although rare, Merkel cell carcinoma's incidence rate is increasing and it is important for dermatologists to keep this entity on their differential as it is highly aggressive and can mimic other skin pathologies,” Hernandez warns.