<s>[INST] context: Cytokeratin 20: *Merkel cell carcinoma (MCC) is a rare, aggressive, primary skin cancer exhibiting neuroendocrine differentiation. oThe 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. oCytogenetic 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 sho arm of chromosome 1are 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 paial trisomy 01 chromosomes 1, 11, 18, and X. Unlike neuroendocrine (small cell) carcinoma of the lung, gene amplifications are rare in cutaneous MCC. oCytokeratin 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. oElectron microscopic findings are char9- cteristic, revealing a lobulated nucleus that may contain rodlets. The cytoplasm is electron- lucent and contains a prominent Golgi apparatus 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. [/INST] question: Merkel cell carcinoma is due to | options: A: Cytokeratin: 7 B: Cytokeratin: 19 C: Cytokeratin: 20 D: Cytokeratin: 18 | answer: C </s>