Pure squamous cell carcinoma of the larynx with cervical nodal metastasis showing rhabdomyosarcomatous differentiation. Clinical, pathologic, and immunohistochemical study of a unique example of divergent differentiation.

We describe a unique case of pure squamous carcinoma of the larynx that developed a cervical lymph node metastasis showing rhabdomyosarcoma admixed with squamous carcinoma (that is, carcinosarcoma). The rhabdomyosarcoma showed foci immunoreactive to multiple cytokeratin monoclonal antibodies, as well as to markers for striated muscle, thus indicating true divergent epithelial and rhabdomyosarcomatous differentiation. Although the morphogenesis of carcinosarcomas remains controversial, the sequence of events for the current case favors sarcomatous transformation of the original carcinoma (that is, sarcomatous neometaplasia of the primary carcinoma clone). The possible contributory role of radiation therapy in this case in inducing such a change is noted.