Merkel cell carcinoma is due to
A. Cytokeratin: 7B. Cytokeratin: 19
C. Cytokeratin: 20
D. Cytokeratin: 18
The
answer is C. Cytokeratin 20:
•
Merkel cell carcinoma (MCC) [trabecular carcinoma, small cell carcinoma of the skin, primary cutaneous
neuroendocrine carcinoma] is a rare, aggressive, primary skin cancer exhibiting
neuroendocrine differentiation.
•
The histogenesis of MCC is controversial. Possible cells
of origin include the epidermal MC, a dermal MC equivalent, a
neural-crest-derived cell of the amine precursor uptake and decarboxylation
(APUD) system, and a residual epidermal stem cell.
•
Cytogenetic abnormalities are present in 30-47% of MCCs.
The most frequent change is loss of heterozygosity due to translocations or
deletions of chromosome 1; specifically, 2 distinct regions in the most distal
band 1 p36 on the short arm of chromosome 1 are implicated in MCC. Similar
abnormalities near this site occur in several neuro cystic tumors, including
melanoma, neuroblastoma, and pheochromocytoma. Other abnormalities described in
MCC include losses at chromosomes 3, 13, and 22 and partial
trisomy 01 chromosomes 1, 11, 18, and X. Unlike neuroendocrine (small cell)
carcinoma of the lung, gene amplifications are rare in cutaneous MCC.
•
Cytokeratin 20 is expressed in a dot like paranuclear or
crescentic pattern; other low molecular weight (MW) cytokeratin antibodies
(E.g., CAM5.2, MNF116), white less specific, react in a similar localization
pattern.
•
Electron microscopic findings are characteristic,
revealing a lobulated nucleus that may contain rodlets. The cytoplasm is
electron-lucent and contains a prominent Golgiapparatus and numerous ribosomes.
Intermediate filaments are numerous and often assume a parallel or whorled
arrangement near the nucleus, accounting for the dot like pattern of cytokeratin
distribution visualized by immunohistochemistry. Desmosomes may be present.
Most diagnostic is the dense core granule (80-120 mn in diameter), the source
and the locus of the neuroendocrine peptides.
