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Case 73 - Discussion

Uploaded: 2008-02-06, Updated: 2008-02-06



CD20 CD79a
CD10 CD3
CK20 Synaptophysin
CD117 Chromogranin A
CK AE1/3  
  • Diagnosis: metastatic Merkel cell carcinoma.

  • Microscopic description: The tumor consists of monotonous, small, round and blue cells with very high N/C ratio and evenly dispersed chromatin. The nucleolus is inconspicuous. The tumor cells are dyscohesive with focal vaguely nodular pattern. Abundant mitotic figures are present.

  • Differential diagnosis:

    • T-ALL: young age, mediastinal mass, TdT+, CD3+.

    • B-ALL: young age, more common as leukemia form, TdT+, CD10+, CD20+.

    • Metastatic small cell carcinoma for the lung: CK20-, CK5/6+, TTF+ (50%), CEA+/-.

    • Small cell melanoma: S100+, MITF+. MART1+, HMB45+, CK20-.

    • PNET: CD99+, Vimentin+, CK20-.

    • Merkel cell carcinoma: CK20+, CK5/6-, p63-, TTF1-, CEA-, S100-, vimentin-, CD45-, CD117+, Synaptophysin+, chromogranin A+.



      PanCK CK20 CK5/6 P63 TTF1 CD99 CEA S100




      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 +/− +/− +