Skin nonmelanocytic tumor
Neural tumors
Merkel cell carcinoma

Topic Completed: 1 June 2012

Revised: 3 December 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Merkel cell carcinoma [title] skin

Christopher S. Hale, M.D.
Page views in 2019: 23,534
Page views in 2020 to date: 1,066
Cite this page: Hale CS. Merkel cell carcinoma. website. Accessed January 18th, 2020.
Definition / general
  • Also called neuroendocrine carcinoma of skin
  • Primary neuroendocrine carcinoma of the skin is a rare malignancy which presents most commonly on sun exposed areas in late adulthood
  • Tumor typically metastasizes quickly with a fatal outcome
  • Originally called trabecular carcinoma
  • May derive from Merkel cell in epidermis, derived from neural crest, important for tactile sensation in lower animals
  • Merkel cell carcinoma often arises in setting of immunodeficiency (posttransplant immunosuppression or HIV infection), autoimmune connective tissue disease and neoplasm, particularly Hodgkin disease, B cell lymphoma, chronic lymphocytic leukemia, breast and ovary cancer
  • Established risk factors for Merkel cell carcinoma development are UV radiation, immunosuppression and Merkel cell polyomavirus infection (Science 2008;319:1096)
Clinical features
  • Classic clinical presentation is a rapidly growing, red to violaceous, firm, solitary nodule
  • Usually adults or elderly
  • 60% women
  • Face and extremities
  • May be associated with squamous cell carcinoma (in situ or invasive), basal cell carcinoma, eccrine duct-like structures
  • Aggressive
  • Regional nodal metastases are common
  • Metastases are usually found in skin (28%), liver (13%), bone (10%), brain (6%) (Postepy Dermatol Alergol 2014;31:325); also testis or other unusual sites
  • Rarely appears to arise initially in lymph node, probably due to regression of primary skin tumor
Case reports
  • Wide surgical excision or Mohs micrographic surgery of tumor with sentinel lymph node biopsy (J Skin Cancer 2013;2013:189342)
  • Adjuvant radiotherapy or chemotherapy according to clinical staging
  • Metastases are treated with protocols similar to those for small cell lung carcinoma
Clinical images

Images hosted on PathOut server:

Hip lesion

Gross description
  • Nodular or ulcerated red-violet lesion
Gross images

Images hosted on PathOut server:

Breast skin, courtesy of Mark R. Wick, M.D.

Hip lesion

Microscopic (histologic) description
  • Dermal or subcutaneous centered tumor with monotonous round tumor cells and diffuse infiltration of subcutis
  • May have focal trabecular pattern
  • Cells have scant eosinophilic cytoplasmic rim, round and vesicular nuclei with finely granular and dusty chromatin and multiple nucleoli
  • Also apoptotic nuclei and frequent mitotic figures
  • May have vascular stroma with plump endothelial cells
  • Epidermis is usually spared
  • Rarely has leiomyosarcoma or atypical fibroxanthoma-like areas
Microscopic (histologic) images

Images hosted on PathOut server:

Breast skin, courtesy of Mark R. Wick, M.D.






Case of the Week #304

Images hosted on other servers:

H&E, 2x

H&E, 10x

H&E, 20x

H&E, 40x

CK20, 40x

NSE, 40x

Dermal solar degeneration

Dark epitheliod neoplastic infiltrates

Vague cell borders




Cytology images

Images hosted on PathOut server:

Giemsa stain, COW #414

Cell PAP, COW #414

Cell block - H&E, COW #414

FNA, CK20+ with perinuclear dot-like
staining, CD45-, TTF-; flow was CD56+, CD45-

Images hosted on other servers:

Paranuclear blue dots, courtesy of Dr. Tim Bracey

Positive stains
Negative stains
Electron microscopy description
  • Dense core neurosecretory granules and tightly packed intermediate filaments
  • Well developed desmosomes
Molecular / cytogenetics description
  • Abnormalities in #1, #11, #12
  • 1p35-36 deletion
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