Biphenotypic sinonasal sarcoma

Classification

• Biphenotypic sinonasal sarcoma
• Original name: Low-grade sinonasal sarcoma with neural and myogenic features, but it is no longer recommended.

• A low-grade spindle cell neoplasm of the sinonasal tract associated with overlying respiratory epithelium and showing S100 protein and actin immunoreactivity.

  Signs and symptoms

Diagnosis

Microscopic

• Infiltrative, highly cellular spindled cell neoplasm that is poorly circumscribed and unencapsulated. Bone destruction or invasion is common. The cells show medium to long fascicles with a herringbone pattern. The cells are remarkably uniform with elongated nuclei. There are delicate strands of intercellular collagen without ropy or dense deposition. There is a very characteristic concurrent surface-type respiratory epithelial proliferation 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

• S100 protein Focal, patchy to diffuse in all tumors.
• Smooth muscle actin or muscle specific actin seen in nearly all tumors, but strong and diffuse reaction with SMA is seen in only about 50% of cases.
• No reactivity with other tumor markers such as SOX10, myogenin, estrogen receptor, progesterone receptor, or keratins.

• t: PAX3-MAML3 fusion protein. Only a few cases have shown a PAX3-NCOA1 ), and the tumor is negative for SS18-SSX1 or SSX2

  Differential diagnoses

• Fibrosarcoma: Can be very similar; although, nerve fibers and herringbone pattern tend to be longer and more well developed
• Synovial sarcoma: Almost histologically identical, but genetic translocation will be shown through FISH or RT-PCR.
• Malignant peripheral nerve sheath tumor such as triton tumor: Distinctive alternating light and dark cellular areas; association with peripheral nerves; usually a high-grade tumor with pleomorphism, necrosis, and increased mitoses. Generally shows reactivity with S100 protein and SOX10 while negative: SMA, MSA
• Leiomyosarcoma: Fascicular architecture, with cigar-shaped nuclei showing blunt ends, perinuclear halos and eosinophilic cytoplasm. Much stronger reactivity with desmin and SMA, while usually negative with S100 protein.
• Mucosal melanoma: Also a spindled cell tumor in many cases, but there is pleomorphism intranuclear inclusions and prominent nucleoli. The neoplastic cells are usually strongly reactive with S100 protein, SOX10, HMB45, Melan-A, tyrosinase, while negative for SMA, MSA.

  Epidemiology

Management

• Surgery, often accompanied by radiation, is the treatment of choice. There is frequent local recurrence but often many years after the initial presentation., there are no regional or distant metastases reported, and no patient has yet died from disease.