Intermediate filament aggregates in mitoses of primary cutaneous neuroendocrine (Merkel cell) carcinoma

Primary cutaneous neuroendocrine carcinomas express different kinds of intermediate filaments and frequently in a 'paranuclear globular' pattern. We have observed the same pattern not only in interphase but also in mitotic cells, which are very frequent in these tumours. We report a quantitative and morphological study of eight primary cutaneous neuroendocrine carcinomas stained with different antibodies against cytokeratins (CAM 5.2 and anti-cytokeratin 20), neurofilaments (70 kDa and 200 kDa) and peripherin. We have found a predominance of CAM 5.2 expression in interphase cells and of neurofilament proteins in mitotic cells; 87.02% of the interphase cells were positive with CAM 5.2 whereas only 6.08% were positive for neurofilaments ( P <0.01); 35.41% of the mitotic cells were positive with CAM 5.2, whereas 50% were positive for neurofilaments ( P <0.01). A correlation between a globular pattern of intermediate filament proteins and prognosis has not been found. We describe for the first time the division of neoplastic cells with a globular pattern; the presence of intermediate filament proteins with a globular pattern in all mitotic stages; and the uneven distribution of this formation between the two daughter cells.