Merkel cell carcinoma of the skin

(primary neuroendocrine cell carcinoma of the skin)

Clinical features

Typically a rapidly growing lesion on sun-damaged skin of the head and neck of the elderly. Clinical diagnoses are commonly erroneous. Merkel cell carcinoma may occasionally occur in the vulva or at extra-cutaneous sites such as the oesophagus or vagina⁹.

Histopathology

Merkel cell tumours are commonly associated with other skin lesions, including actinic keratoses, Bowen's disease, squamous cell carcinomas and basal cell carcinomas.

Immunohistochemistry

	monokeratin 27/275 (dot-like) Pancytokeratin 1/1 (vaginal Merkel cell carcinoma)9 CK5/6 0%7 CK7 17%7, 0/1 (vaginal Merkel cell carcinoma)9 CK8/18 9/116 CK20 33/341,16/212, 16/183,23/234, 2/25, 10/116, 87%7, 1/1 (vaginal Merkel cell carcinoma)9 NSE 24/255, 1/1 (vaginal Merkel cell carcinoma)9 Chromogranin 11/205, 1/1 (vaginal Merkel cell carcinoma)9 S-100 0/265, 0/1 (vaginal Merkel cell carcinoma)9 HMB-45 0/95, 0/1 (vaginal Merkel cell carcinoma)9 EMA 5/55, 1/1 (vaginal Merkel cell carcinoma)9 Vimentin 1/125 CD45 0/135 TTF-1 0/212, 0/183, 0/234, 0/116, 0/1 (vaginal Merkel cell carcinoma)9 pax-5 29/31 (4 diffuse strong, 13 diffuse moderate, 11 diffuse weak, 1 focal moderate. 3 cases subjected to flow cytometry were negative for CD19)8 serotonin 0/15 thyroglobulin 0/15 synaptophysin 0/15, 0/1 (vaginal Merkel cell carcinoma)9 oestrogen receptor 0/15 progesterone receptor 0/15 prostate specific antigen 0/25 bcl-2 1/1 (vaginal Merkel cell carcinoma)9 CD10 0/1 (vaginal Merkel cell carcinoma)9 CD45 0/1 (vaginal Merkel cell carcinoma)9 CD56 0/1 (vaginal Merkel cell carcinoma)9 CD117 1/1 (vaginal Merkel cell carcinoma)9

Differential diagnosis

metastatic small cell carcinoma from a primary in the lung or other site

• granulocytic sarcoma

• small cell malignant melanoma

Prognosis

Poor: in one series, 60% of patients had local recurrences or metastases at follow up⁵. Regional metastases occur in up to 75% of patients. Five year survival is between 30% and 64%.

References

¹ Chan JKC et al. Cytokeratin 20 immunoreactivity distinguishes Merkel cell (primary cutaneous neuroendocrine) carcinomas and salivary gland small cell carcinomas from small cell carcinomas of various sites. Am J Surg Pathol 1997;21:226-234.

² Bryd-Gloster A et al. Differential expression of thyroid transcription factor 1 in small cell lung carcinoma and Merkel cell tumor. hum Pathol 2000;31:58-62.

³ Ordonez NG. Value of thyroid transcription factor-1 immunostaining in distinguishing small cell lung carcinomas from other small cell carcinomas. Am J Surg Pathol 2000;24:1217-1223.

⁴ Cheuk W et al. Immunostaining for thyroid transcription factor-1 and cytokeratin 20 aids in the distinction of small cell carcinoma from Merkel cell carcinoma, but not pulmonary from extrapulmonary small cell carcinoma. Arch Pathol Lab Med 2001;125:228-231.

⁵ Walsh, N. M. Primary neuroendocrine (Merkel cell) carcinoma of the skin: morphologic diversity and implications thereof. Hum Pathol 2001;32:680-689.

⁶ Leech, S. N., Kolar, A. J., Barrett, P. D., Sinclair, S. A., Leonard, N. Merkel cell carcinoma can be distinguished from metastatic small cell carcinoma using antibodies to cytokeratin 20 and thyroid transcription factor 1. J Clin Pathol 2001;54:727-729

⁷ Erickson, L. A. and R. V. Lloyd (2004). "Practical markers used in the diagnosis of endocrine tumors." Adv Anat Pathol 11(4): 175-89.

⁸ Dong HY, Liu W, Cohen P, et al. B-cell specific activation protein encoded by the PAX-5 gene is commonly expressed in merkel cell carcinoma and small cell carcinomas. Am J Surg Pathol 2005; 29:687-92

⁹ Coleman NM, Smith-Zagone MJ, Tanyi J, et al. Primary neuroendocrine carcinoma of the vagina with Merkel cell carcinoma phenotype. Am J Surg Pathol 2006; 30:405-10

This page last revised 17.4.2006.