Spindle Cell Carcinoma

osteosarcomatous, chondrosarcomatous, or rhabdosar-comatous differentiation may be present, particularly in patients who had been previously treated by radiotherapy [203, 213, 356]. Sometimes, only spindle cells are present; in such cases, a SpCC can be mistaken for a true sarcoma.

However, occasional cases of SpCC may be less cellular, closely resembling a reactive fibroblastic proliferation and can thus be mistaken for a pseudosarcoma-tous reaction in a SCC or for radiation-induced stromal atypia [13].

Metastases usually contain SCCs alone or both SCC and spindle cell components, and rarely, only a spindle cell component [205, 232, 340].

Electron microscopy has revealed evidence of epithelial differentiation in spindle cells, such as desmosomes and tonofilaments [33, 151, 349, 391].

Immunohistochemically, tumour cells in SpCC often express epithelial and mesenchymal markers; moreover, keratin and vimentin coexpression has been observed on individual tumour cells [241, 391]. Cytokeratin expression can be demonstrated in spindle cells in 4085.7% of cases (Fig. 1.14c), depending on the number of antikeratin antibodies used [96, 241, 329, 349, 360, 391]. The most sensitive/reliable epithelial (keratin) markers for SpCC seem to be keratin (AE1/AE3, K1) K1, K18 and epithelial membrane antigen (EMA) [356].

Spindle cells always express vimentin and often other mesenchymal filaments, such as myogenic markers (smooth muscle actin, muscle specific actin, desmin). The presence of S-100 protein has been reported in rare cases of SpCC [356]. SpCCs do not express glial-fibril-lary acid protein (GFAP), chromogranin or HMB-45 [356]. p63 has been recently suggested as an alternative epithelial marker in SpCCs [213a].

The diagnosis of a SpCC is based on the demonstration of an invasive or in situ SCC and a malignant spindle cell component. However, when a SCC component cannot be demonstrated, the diagnosis is more difficult, and the SpCC must be distinguished from a number of benign and malignant processes, such as spindle cell sarcomas, nodular fasciitis, inflammatory myofibroblastic tumour and malignant melanoma.

In the head and neck, true sarcomas (with the exclusion of chondrosarcomas) and benign mesenchymal tumours are very rare; if present, they are usually located in deep structures [356]. It is therefore a general view that in the mucosa of the upper aerodigestive tract a malignant spindle cell tumour is probably a SpCC and not a sarcoma.

Negative reaction for S-100 protein and HMB45 helps to distinguish SpCCs from malignant melanomas [96].

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