Small cell neuroendocrine carcinoma with skeletal muscle differentiation -Report of three cases

Three cases of neuroendocrine carcinoma showing skeletal muscle differentia tion are presented. The tumors were located in the skin and subcutaneous ti ssue, the urinary bladder, and the nasal cavity respectively, and were comp osed by two cell types admired intimately with each other. One cell type ha d features identical to those seen in conventional small cell neuroendocrin e carcinoma, including scanty cytoplasm, round nuclei with fine granular ch romatin, immunohistochemical reactivity for neuron-specific enolase, chromo granin and cytokeratins, and electron-dense granules on ultrastructural exa mination. The second cell: type was either plasmacytoid or elongated and st raplike, with-abundant eosinophilic cytoplasm and irregular nuclei with pro minent nucleoli. These cells showed immunohistochemical positivity for desm in, sarcomeric actin, myoglobin, and myogenin. They also exhibited ultrastr uctural evidence of rhabdomyoblastic differentiation in the form of contrac tile filaments with abortive Z-band formation. An origin from a cell capabl e of dual differentiation toward neuroendocrine and rhabdomyoblastic elemen ts is postulated for these tumors.