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AT-A-GLANCE

AT-A-GLANCE

  • The risk of death from Merkel cell carcinoma (MCC) is 2 to 3 times higher than from melanoma.

  • Reported incidence of MCC quadrupled from 1986 to 2006.

  • Risk factors for MCC include advanced age, immune suppression, and fair skin.

  • Merkel cell polyomavirus (MCPyV) is integrated in 80% of MCC cases.

  • Consider MCC in the differential diagnosis of any rapidly growing, nontender nodule on a sun-exposed area.

  • Management is challenging as therapy is unique and controversial.

  • Sentinel lymph node biopsy, surgery, and radiation are indicated in many cases.

  • Imaging (CT, MRI, positron emission tomography) has poor sensitivity and specificity in early stages of MCC, but can be useful in assessment of and surveillance for metastatic disease.

  • MCC is an especially radiosensitive tumor. Adjuvant radiation therapy is highly effective, and overaggressive surgery should be avoided. Radiation monotherapy is an important and effective option for managing disease in patients who are not candidates for surgery.

  • Immune therapies, including checkpoint inhibition and T-cell therapies are now the treatment of choice for advanced disease.

  • Chemotherapy has very limited utility in treating MCC, and adjuvant chemotherapy is not beneficial. Adjuvant immune therapy is an area of new research.

  • Optimal care includes multidisciplinary coordination between dermatologists, surgeons, radiologists, and medical oncologists with reference to the National Comprehensive Cancer Network (NCCN) guidelines.

Merkel cell carcinoma (MCC) is an increasingly common neuroendocrine skin cancer that is associated with ultraviolet (UV) light exposure, advanced age, immune suppression, and the Merkel cell polyomavirus (MCPyV). The reported incidence of MCC has more than tripled in the past 20 years1 to approximately 1500 U.S. cases/year,2 and is expected to grow with the aging population. Although it is 40 times less common than malignant melanoma, it carries a markedly poorer prognosis, with disease-associated mortality at 5 years of 46%3 as compared with 9% for invasive melanoma.4 Management of MCC is controversial as optimal therapy is rapidly evolving with promising immune therapy options.

HISTORICAL PERSPECTIVE

MCC is a relatively recently described entity, although the Merkel cell was identified more than 100 years ago. In 1875, human Merkel cells were first described by Friedrich S. Merkel (1845-1919). He named these cells Tastzellen (touch cells) assuming that they had a sensory touch function within the skin because of their association with nerves. In 2009, a series of studies using mouse models resolved several longstanding debates by conclusively establishing that (a) Merkel cells are essential for light touch responses,5 (b) Merkel cells have an epidermal origin,5,6 and (c) Merkel cells do not divide, but are renewed by a reservoir of epidermal progenitor cells.6

In 1972, Toker described 5 cases of “trabecular cell carcinoma of the skin,” consistent with what we now call MCC. In 1978, Tang and Toker found that cells from these tumors contained dense core granules on electron microscopy that were typical of Merkel cells ...

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