Answer: Spindle cell squamous carcinoma (carcinosarcoma)

Histology: This case represents an unusual form of spindle cell carcinoma. Although areas of clear-cut squamous differentiation are present, the majority of the epithelial component of the tumor has pronounced features of the basaloid variant of squamous cell carcinoma. In addition, the spindle cell component of the neoplasm has a pronounced storiform pattern in areas and also contains osteoclast-like stromal giant cells.

Discussion: The spindle cell variant of squamous carcinoma often has a polypoid growth pattern as seen here. A characteristic lesion microscopically shows very prominent spindle cell or sarcoma-like stroma with only a minor component of conventional squamous cell carcinoma. Because of the spindle cell areas, the terms sarcomatoid carcinoma, pseudosarcoma, or carcinosarcoma have been applied to these lesions. Most investigators now accept the idea that these are fundamentally carcinomatous neoplasms that have acquired divergent mesenchymal differentiation. The authors of the AFIP fascicle (see reference) suggest that the term pseudosarcoma be particularly avoided because of possible confusion with benign “sarcoma-like” processes. The stromal component of these lesions may have a variety of confusing appearances; widely dilated, branching blood vessels may suggest an hemangiopericytoma, or, as in our case, highly pleomorphic stromal cells may intersect in a storiform pattern that suggests a malignant fibrous histiocytoma. In other cases areas of overt osteoid or cartilage formation may be seen. Immunocytochemically biphasic spindle cell carcinomas usually show immunoreactivity for cytokeratin in the spindle cell component. In other cases, some muscle markers (actin) may be positive. Electron microscopic studies usually show focal epithelial features in the spindle cell component.

The differential diagnosis of this type of spindle cell neoplasm in the head and neck has been simplified by the acceptance of the idea that all, or at least most, of these lesions are really spindle cell carcinomas. Mucosal malignant melanoma is an important consideration in the differential diagnosis of any spindle cell neoplasm involving the mucosal membranes of the head and neck. Immunohistochemical studies (S-100 protein, HMB45, Melan-A) coupled with epithelial markers aid in this distinction. If rhabdomyosarcoma is a serious consideration, use of immunostains for myogenin or desmin may be helpful, if coupled with negative epithelial markers. The rate of metastasis depends on the primary location of the lesion and the hypopharyngeal tumors have a high (60+%) rate of metastasis. While some studies initially suggested that only the carcinomatous component was capable of metastasis, spread of the spindle cell elements has been well documented.