Immunohistochemical and molecular genetic approaches to soft tissue tumor diagnosis: a primer

During the past two decades we have witnessed the identification of an expanding list of immunohistochemical and molecular markers linked to histopathologically defined subtypes of tumors. These markers offer new insights and approaches to the classification of tumors with important prognostic and/or therapeutic implications. We review the potentially diagnostic immunohistochemical and molecular markers of soft tissue tumors (STTs). The immunohistochemical markers reviewed include vimentin, cytokeratin, desmin, HHF35, S100, myoD1, alpha1-antitrypsin, vascular markers (factor VIII, CD31, CD34), MIC2, and others. The potentially diagnostic chromosomal translocations and associated genes identified in STT include Ewing's/PNET t(11;22)(q24;q12)(FLI1;EWS), t(21;22)(q22;q12)(ERG; EWS); t(7;22)(p22;q12)(ETV1;EWS); desmoplastic small round cell tumor t(11;22)(p13;q12)(WT1;EWS); extraskeletal myxoid chondrosarcoma t(9;22)(q22;q12) (TEC(CHN);EWS); malignant ectomesenchymoma t(11;22)(q24;q12)(FLI1;EWS); alveolar rhabdomyosarcoma t(2;13)(q35;q14)(PAX-3;FKHR); t(1;13) (p36;q14)(PAX-7;FKHR); myxoid and round cell liposarcoma t(12;16)(q13;p11)(CHOP;TLS(FUS)); synovial sarcoma t(X;18)(p11;q11)(SSX1&2;SYT), and others. The nature, utility, and limitations of these markers in diagnostic settings are explored.