Rhabdomyosarcoma

Characteristic fusion gene abnormalities are present in adenovascular rhabdomyosarcoma (AlveolarRMS), such as PAX3-FOXO1 (t(2;13)(q35;q14), 75% incidence), PAX7-FOXO1 (t(1;13)(p36;q14), 25% incidence), PAX3-AFX (t(X;2)( q13;q35));

Adenovascular rhabdomyosarcoma is primarily differentiated from adenocarcinoma, angiosarcoma, synovial sarcoma, adenovascular soft tissue sarcoma, Ewing's sarcoma, lymphoma, and small-cell carcinoma.The PAX3 gene breakthrough probe can be used to test for fusions to partner genes, and children with a positive PAX fusion have a particularly poor prognosis;

In biphasic synovial sarcoma about half of all cases are associated with PAX3 PAX3-MAML3 fusion in about half of the cases of biphasic synovial sarcoma;

In biphasic nasal sinus sarcomas with characteristic PAX3 gene translocations, more than half of them have PAX3-MAML3 fusions; in a small percentage of patients, PAX3-NCOA1 and PAX3-FOXO1 fusions may also be present; and about 20% of the patients have fusions of other unknown partner genes with PAX3. This tumor is mainly distinguished from monophasic synovial sarcoma and MPNST.

Undifferentiated-Unclassified Sarcoma

Characteristic PAX3 gene translocations are associated with biphenotypic nasal sinus sarcoma (BSNS), in which more than half of the patients have a PAX3-MAML3 fusion; in a small percentage of patients, they may also have a PAX3-NCOA1 and a PAX3-FOXO1 fusion; and in about 20% of the patients, they have fusions of other unknown partner genes with PAX3. BSNS is a unique low-grade malignant tumor of the nasal sinuses with dual neural and myogenic differentiation that is easily confused with other spindle cell tumors. This tumor is primarily differentiated from monophasic synovial sarcoma and MPNST.Disruption of the PAX3 gene is the gold standard for diagnosis of this tumor, and PAX3 is positively expressed in BSNS with limited specificity.The PAX8-OTI6H8 antibody is also expressed in BSNS, and neither of the PAX8-EP298 antibodies are expressed.