Answer: Squamous cell carcinoma, spindle cell type (sarcomatoid carcinoma)

Histology: The specimen consists of a polypoid fragment of tissue. The surface is lined by partially ulcerated squamous epithelium with changes of high grade dysplasia (carcinoma in-situ). The underlying stroma is loose and myxoid. It contains singly dispersed bizarre atypical cells with enlarged hyperchromatic nuclei and ample cytoplasm. Mitotic figures, including atypical forms, are easily identified. The stromal component was found to be negative for a panel of cytokeratin immmunoperoxidase stains with the exception of focal staining with 34BE12.

Discussion: The spindle cell variant of squamous cell carcinoma (sarcomatoid carcinoma, SC) is a tumor derived from the squamous-lined epithelium that shows divergent differentiation along mesenchymal lines. Not surprisingly, its light microscopic appearance may closely resemble a true sarcoma or an inflammatory pseudotumor. The only assured means of diagnosing a sarcomatoid carcinoma is to identify a more conventional squamous carcinoma in association with the sarcomatoid component. As in the present case, this may take the form of dysplasia of the overlying epithelium. Most sarcomatoid carcinomas present as exophytic polyps, and in many cases the surface epithelium is entirely ulcerated. A residual component of squamous carcinoma and/or dysplasia may be found at the base of the ulcer or stalk of the polyp. A conventional carcinomatous component may not be identified in about 1/3 of all cases. In these instances, electron microscopy and/or immunohistochemistry may be helpful in establishing the epithelial nature of the sarcomatoid proliferation. Absence of cytokeratin staining, however, does not necessarily exclude the diagnosis of sarcomatoid carcinomas. In my experience and the experiences of others, about 30% of these tumors are not immunoreactive for cytokeratin.

Sarcomatoid carcinoma must also be distinguished from a myofibroblastic pseudotumor, vocal cord polyp with stromal atypia, and carcinoma with a pseudosarcomatous stroma. This dilemma is especially challenging for tumors that are not immunoreactive for cytokeratin. If the stromal cells are truly malignant, they should exhibit overtly malignant cellular features including increased mitotic activity and atypical mitotic forms.