Case 7 - Discussion

Uploaded: 2007-01-11, Updated: 2007-11-30

CK20, 4×

CK20, 40×
   
 

Merkel Cell Carcinoma

The Key Features

  • Small blue round uniform tumor cells;

  • CK20, Perinuclear globules.

Clinical Futures
 

  • Also named primary neuroendocrine carcinoma of the skin;

  • Predilection for the head and neck of older adults, sun-exposed area;

  • Distant metastasis in 40% patients.

Gross Findings
 

  • Pink-red or violaceous, firm, dome-shaped solitary rapidly growing nodule.

Microscopic Findings
 

  • Sheet-like, nested, trabecular growth

  • Monotonously uniform, small, round to oval; finely dispersed chromatin; nucleoli not prominent; Scant cytoplasm and faintly amphophilic;

  • Abundant mitoses; Extensive necrosis and individual cell necrosis;

  • Delicate fibrovascular stroma.

Differential Diagnosis
 

Tumor

 PanCK CK20 CK5/6 P63 TTF1 CD99 CEA S100

Melan-A

 Vimentin

CD45
Merkel cell carcinoma + + − − − +/− − − − − −
Metastatic small cell carcinoma (lung) + − − − + +/− +/− − − − −
Small cell squamous carcinoma + − + + − − − − − +/− −
Small cell eccrine carcinoma + − − − − − +/− +/− − +/− −
Small cell melanoma − − − − − +/− − + + + −
Primitive neuroectodermal tumor +/− − − − − + − − − + −
Non-Hodgkin's Lymphoma − − − − − +/− − − − +/− +

Immunohistochemistry Straining
 

  • Perinuclear globule with low molecular weight CK;

  • Positive: CK20, NSE, chromogranin, synaptophysin, somatostatin, calcitonin, VIP, CD117;

  • Negative: S-100, CEA, TTF1

Election Microscopy
 

  • Paranuclear whorls of intermediate filaments;

  • Membrane-bound dense-core secretory granules.

Treatment and Prognosis
 

  • Very aggressive tumor.

Reference
 

  • AFIP, non-melanocytic tumors of the skin, series 4;