Microscopic Hematoxylin and eosin stained image of a<unk>  * Infiltrative, highly cellular spindled cell neoplasm is poorly circumscribed and unencapsulated. Bone destruction or invasion is common. The cells show medium to long fascicles (nerve fibers), with a herringbone pattern. The cells are remarkably uniform with elongated nuclei. Delicate strands of intercellular collagen without ropy or dense deposition are seen. A very characteristic concurrent surface-type respiratory epithelial proliferation is found from the surface or in small cystic spaces around the cancer cells, often forming glands. The background may have a rich vascularity and usually has a small number of scattered lymphocytes. Extra growths or mitoses are rare, while necrosis, ulceration, and hemorrhage are usually absent. Ancillary tests *Immunohistochemistry * S100 protein (a tumor marker protein) is focal, patchy to diffuse in all tumors. S100 protein reaction in a<unk>  * Smooth-muscle actin or muscle-specific actin is seen in nearly all tumors, but a strong and diffuse reaction with SMA is seen in only about 50% of cases. Smooth-muscle actin reaction in a<unk>  * No reactivity occurs with other tumor markers such as SOX10, myogenin, estrogen receptor, progesterone receptor, or keratins. *Genetic testing * t(2;4)(q35;q31.1): PAX3-MAML3 fusion protein Only a few cases have shown a PAX3-NCOA1 (inv(2)(q35p23)), and the tumor is negative for SS18-SSX1 or SSX2 Differential diagnoses * Fibrosarcoma can be very similar, although nerve fibers and the herringbone pattern tend to be longer and more well developed. * Synovial<unk>  is almost histologically identical, but genetic translocation (SS18-SSX1 or SSX2) is shown through fluorescence in situ hybridization or RT-PCR. * Malignant peripheral nerve sheath tumor, such as triton tumor, has distinctive alternating light and dark cellular areas, an association with peripheral nerves, and usually a high-grade tumor with pleomorphism, necrosis, and increased mitoses. Generally, it shows reactivity with S100 protein and SOX10, while negative for SMA or MSA. * Leiomyosarcoma has fascicular (nerve tract) architecture, with cigar-shaped nuclei showing blunt ends, perinuclear halos (cellular nuclear shrinking), and eosinophilic cytoplasm. Much stronger reactivity occurs with desmin and SMA, while it is usually negative with S100 protein. * Mucosal melanoma, also a spindled-cell tumor in many cases, has pleomorphism (more variety in shape/size of tumor cells), intranuclear inclusions, and prominent nucleoli. The neoplastic cells are usually strongly reactive with S100 protein, SOX10, HMB45, Melan-A, and tyrosinase, while negative for SMA or MSA. Epidemiology == As it is newly described, this tumor is probably under-reported, though it is considered to be very rare. Patients present over a wide age range (24–85 years), with a mean age of 52 years. More females are diagnosed than males (3:1).
Biphenotypic sinonasal sarcoma
Sinonasal undifferentiated carcinoma
Nesidioblastoma
Nasopharyngeal angiofibroma
Lymphoepithelioma
Medulloepithelioma
Nasal glioma
Reticulohistiocytoma