DIAGNOSTIC UTILITY OF MIC-2 IMMUNOCYTOCHEMICAL STAINING IN THE DIFFERENTIAL-DIAGNOSIS OF SMALL BLUE CELL TUMORS

Ewing's sarcoma (ES) and peripheral neuroectodermal tumor (PNET) ale c onsidered irt the differential diagnosis of small round blue cell tumo rs of infancy and childhood which includes neuroblastoma, rhabdomyosar coma and malignant lymphoma. Fine-needle aspiration diagnosis of these neoplasms can be particularly difficult when the neoplasms are compos ed of poorly differentiated cells or fail to produce a stroma. MIC-2 i s a highly sensitive and specific marker for the PNET/ES group of neop lasms and has been studied extensively in surgical pathology. Other sm all blue cell neoplasms including rhabdomyosarcoma, blastemal Wilm's t umor and lymphoblastic lymphoma have also shown positivity but the sta ining reactions are usually weak and focal. The utility of this marker in the differential of small blue cell neoplasms in cytologic materia l has not been examined. Twenty cases of small blue cell neoplasms obt ained by fine-needle aspiration (FNA),I ere studied. MIC-2 antibody,wa s applied retrospectively to formalin-fixed cell black material and de stained alcohol-fired and air-dried cytologic preparations. These case s include primitive neuroectodermal tumor (five cases), Ewing's sarcom a (two cases), neuroblastoma (four cases), Wilms's armor (four cases), lymphoblastic lymphoma (two cases), and small-cell carcinoma (three c ases). The cases were judged positive when the majority of the cells s howed cytoplasmic staining. Diffuse cytoplasmic staining was observed in all seven cases of PNET/ES. Staining could be seen on the destained air-dried smears (three cases), fired smears (two cases), or the cell block material (two cases). None of the other 13 small blue cell neop lasms showed positive staining. We conclude that MIC-2 is a sensitive and specific marker for the PNET/ES group of neoplasms ill specimens f rom formalin-fixed cell block, air-dried, and alcohol-fixed cytologic material and is useful in the differential diagnosis of small blue cel l tumors. (C) 1998 Wiley-Liss,Inc.