Merkel Cell Carcinoma: A Case Report and Brief Review of the Literature

Jordan Isenberg,¹ Tessa Weinberg,² Nowell Solish,^3
1McGill University, Faculty of Medicine, Montreal, Quebec; ²The Royal College of Surgeons in Ireland, Faculty of Medicine, Dublin, Ireland;
³University of Toronto, Department of Dermatology, Toronto, Ontario.

Abstract
Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous malignancy. It is seen most frequently in those over 60 years old and in Caucasian males. It usually presents as an asymptomatic rapidly growing violatious nodule on a sun exposed area. The mainstay of treatment is surgical by standard wide local excision or MOHs chemosurgery. Radiation is added frequently for local control. The only factor significantly associated with overall survival is the stage of disease at presentation. This stresses the importance of early diagnosis and treatment.
Key Words: Merkel cell carcinoma, wide local excision, MOHs chemosurgery, adjuvant radiotherapy, review, case.

Introduction
Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous malignancy. Its cell of origin, the Merkel cell (MC), was first described in 1875 by Freidrich Merkel.¹
Merkel cells are neuroendocrine cutaneous cells, which are not numerous and concentrated in touch sensitive areas, and in glaborous and hairy skin.1 They are located within an intense epidermal sensory network in close association with slowly adapting type 1 mechanoreceptors which are known as MC-neurite complexes or Merkel discs.¹
Cyril Toker described five cases of "trabecular carcinomas of the skin" in 1972² that was named MCC in 1980 following ultrastructural studies.³ There are two hypotheses postulating the MC origin and subsequently that of MCC. The MC is thought to either differentiate from epidermal keratinocyte-like cells or, as with melanocytes, from stem cells of neural crest origin that migrated during embryogenesis.¹

These theories have led to many names being proposed including: neuroendocrine cancer of the skin, small cell carcinoma of the skin and anaplastic cancer of the skin.⁴ A recently recognized oncogenic virus—Merkel cell polyomavirus (MCV)—may be a contributing factor in the pathogenesis of MCC.⁵

Incidence
MCC is a rare skin malignancy with incidence calculations based on United Sates (US) Surveillance, Epidemiology, and End Results (SEER) database report incidence of 0.23 per 100,000 for Caucasians,⁶ a number similar to an estimate using the defined patient population of the Mayo Clinic;⁷ about 470 new cases are diagnosed annually in the US.⁸

Overall MCC is more common in whites (94%) than blacks (1%), in those of advanced age (average 72 years), and in men than women (1.6-2.3:1). Men are also younger at diagnosis (71 years) compared to women (76 years).⁹ Hodgson suggests that the MCC incidence rates have increased threefold over the 1986-2001 period.¹⁰

Case presentation
A 75 year-old Caucasian male patient was referred to our hospital from his primary care physician for management of a rapidly growing mass on the right temple. Past medical and surgical history was noncontributory. Physical exam revealed a tumour; a large, violacious, solid, firm mass measuring 4 cm in diameter and 3 cm in height. The differential diagnosis included Malignant Melanoma, and Kaposi's sarcoma and other non melanoma skin cancers.

The patient underwent complete and wide local excision of the tumour with 2 cm margins radially and periosteum on the deep margin. Microscopic examination showed a tumour composed of small uniformly sized blue neoplastic cells with round oval nuclei, scant cytoplasm, distinct nuclear membranes, finely dispersed nuclear chromatin, and inconspicuous nucleoli. Mitotic figures and individually necrotic cells were present.

The neoplastic cells showed positivity for cytokeratin 20 (CK20) in a perinuclear dot-like fashion, para keratin and synaptophysin. TTF-1 was negative. On the basis of immunohistochemical staining, the diagnosis of Merkel cell carcinoma was made. Lateral margins were clear, depth was clear with in 5 mm.
Laboratory work-up including complete blood count, renal, bone, hepatic and coagulation were all within normal limits. Computed tomography (CT) scan did not show any regional lymphadenopathy.

Radiation oncology was consulted given that the size and depth of the lesion. Radio-therapy was booked three weeks status post WLE.