Answer: Giant pharyngeal atypical lipomatous tumor

Histology: The tumor is present as a large (4 cm) pedunculated polyp of mostly fat and lined by unremarkable squamous epithelium. The lipomatous core is compartmentalized into lobules by thin fibrous bands. Within the fat and fibrous bands are cells with enlarged, hyperchromatic and sometimes multilobated nuclei. By immunohistochemistry, these atypical cells demonstrate nuclear expression of MDM2.

Discussion: Large stromal polyps with cores of fibroadipose tissue are sometimes encountered in the esophagus and hypopharynx. Those lesions that exhibit atypical cells have been problematic in terms of classification. Some have been reported these as well-differentiated liposarcomas or atypical lipomatous tumors; but unlike well differentiated liposarcomas of the deep soft tissues, they rarely recur and do not undergo dedifferentiation despite the fact that they are generally treated by polypectomy alone. Atypical lipomatous tumor/well-differentiated liposarcoma is characterized by the amplification of MDM2 and CDK4 genes on chromosome 12q15 and 12q14. The availability of immunohistochemical markers for MDM2 amplification now permits the sensitive and specific recognition of the MDM2 amplification, and the reliable distinction between atypical lipomatous tumor/well-differentiated liposarcomas and lipomas.

The finding of MDM2 in this and other cases provides strong support that the giant hypopharyngeal lipomatous tumor is in fact a liposarcoma rather than a giant fibrovascular polyp that simply displays atypical degenerated cells. The fact that these tumors do not undergo dedifferentiation likely reflects the fact that they typically come to medical attention and are removed as relatively small lesions (compared to their massive counterparts in the retroperitoneum). Accordingly, they are best regarded as giant pharyngeal atypical lipomatous tumors.