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Case 242 - Discussion

Uploaded: 2011-11-18, Updated: 2011-11-18




Other markers:

CK7   Negative

CD20    Negative




Diagnosis: nodal Merkel cell carcinoma (neuroendocrine carcinoma).

This patient had no history of skin primary.


Nodal Merkel Cell Carcinoma

  • In extraordinarily rare circumstances, nodal Merkel cell carcinoma (or neuroendocrine carcinoma) may arise in the lymph node without associated skin primary before and after diagnosis. These tumors show similar to histological and immunohistochemical features to the skin counterpart.

  • 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+, 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 +/− +/− +