Trisomy 6 in Merkel cell carcinoma: a recurrent chromosomal aberration

We retrospectively investigated 17 cases of primary and metastasizing Merke l cell carcinomas (MCC) from 14 patients using chromosomal in-situ hybridiz ation (CISH) to study the occurrence of trisomy 6 in these lesions. Methods and results: Histological diagnosis on all tumour samples was obtai ned on haematoxylin and eosin stained sections. Immunohistochemistry was pe rformed with antibodies against pancytokeratin (CAM 5.2), cytokeratin 20 (C K20), MIC2 antigen (CD99), neuron-specific enolase (NSE), and chromogranin A (chrA). Sections (4 mum) of the paraffin-embedded tumours were analysed w ith alpha -satellite centromeric probes for chromosome 6 or 17 using CISH. The signal was amplified by the Tyramide Signal Amplification (TSA) assay. Immunohistochemically, the tumours showed the same general epithelial neuro endocrine pattern: 11/13 expressed cytokeratin 20, and 47% exhibited trisom y 6, with no significant difference between primary and metastatic lesions. Incomplete follow-up data did not allow us to establish a prognostic value of trisomy 6, however, this aberration might be an additional diagnostic t ool in distinguishing MCC from other small round blue cell tumours. Conclusions: CISH seems to be a promising adjunctive method to diagnose Mer kel cell carcinoma. Trisomy 6 should be investigated more closely in these cases, as has been done for chromosomes 1 and 11. Of particular interest wo uld be identification of modifications in proto-oncogene(s) located on chro mosome 6.