Spindle-cell carcinoma of the oral cavity and larynx. Immunohistochemical aspects.

Five cases of monophasic and 7 cases of biphasic spindle-cell carcinomas were analyzed immunohistochemically for the presence of vimentin and keratin type intermediate filaments in the pleomorphic spindle cells. Vimentin reactivity proved to be a consistent feature but keratin reactivity was more variable, this latter filament being lost in two cases initially presenting as pure squamous cell carcinomas showing dedifferentiation towards a pure monophasic spindle-cell tumour when recurring. The converse was also noted: acquisition of keratin in a monophasic spindle-cell tumour that recurred as squamous cell carcinoma. These results were considered to support the concept that spindle-cell tumours of the upper aerodigestive tract are a peculiar type of carcinoma and not a product of a pluripotent stem cell exhibiting bidirectional differentiation. Diagnostic implications are as follows: keratin positivity in a spindle-cell tumour substantiates its carcinomatous nature but its absence does not rule out a diagnosis of spindle-cell carcinoma.