IMMUNOHISTOCHEMICAL PROFILE OF MONOCLONAL-ANTIBODY O-13 - ANTIBODY THAT RECOGNIZES GLYCOPROTEIN P30 32(MIC2) AND IS USEFUL IN DIAGNOSING EWINGS-SARCOMA AND PERIPHERAL NEUROEPITHELIOMA/

Ewing's sarcoma (ES) and peripheral neuroepithelioma (PN) are closely related tumors, and it can be difficult to distinguish them from other small-round-cell tumors (SRCTs). The glycoprotein p30/32(MIC2) is hig hly, but not exclusively, expressed in both ES and PN. Although the mo noclonal antibody (Mab) HBA71, which reacts with p30/32(MIC2), has bee n reported to be relatively specific and highly sensitive for both neo plasms, it is not readily available. Yet, Mab O13 is commercially avai lable, and it purportedly displays the same immunostaining characteris tics as HBA71. Because O13 has not been studied extensively, we immuno stained 21 ES/PNs and 147 other tumors or lesions that might show SRCT -like features with O13. The results were similar to those reported fo r HBA71. We found O13 to be 100% sensitive for ES/PN; and, no immunost aining was noted on the SRCTs often included in the differential diagn osis of ES/PN (i.e., conventional neuroblastoma, rhabdomyosarcoma, and nonlymphoblastic lymphomas). But, O13 immunoreacted with lymphoblasti c lymphomas and some other tumors and normal tissues. Nonetheless, thi s nonspecific reactivity should not cause diagnostic problems, if an a ntibody panel containing anti-desmin and anti-leukocyte common antigen is used in conjunction with O13. We conclude that, within the proper diagnostic context, strong immunoreactivity of a SRCT tumor for O13 sh ould be considered good evidence that the tumor is ES/PN.