CD31 immunoreactivity in small round cell tumors

CD31 has been shown to be a sensitive and specific marker for endothelial d ifferentiation among epithelioid and spindled-pleomorphic human neoplasms. However, the role of this marker in the evaluation of small round cell tumo rs has not been evaluated. Formalin-fixed, paraffin-embedded tissue section s from 276 small round cell tumors, including 85 Ewing's sarcoma/primitive neuroectodermal tumors (ES/PNET), 52 rhabdomyosarcomas, 10 extraabdominal p olyphenotypic small cell tumors, six desmoplastic small cell tumors, 11 neu roblastomas, 23 Wilms' tumors, 20 retinoblastomas, 13 esthesioneuroblastoma s, and 56 small cell malignant lymphomas were stained with CD31 (JC/70A, 1: 40), using a modified avidin-biotin-peroxidase complex technique, after cit rate buffer microwave epitope retrieval. Among nonlymphoid small round cell tumors, four of 85 ES/PNET were at least focally reactive. No other lesion in this group was positive. In contrast, the majority of well-differentiat ed (11 of 17), intermediately differentiated (two of three), and lymphoblas tic lymphomas (three of three) were positive. Small cleaved lymphomas (thre e of 13 follicular, one of 13 diffuse) were less often reactive, whereas sm all noncleaved lesions were negative. Although reactivity for CD31 in ES/PN ET is uncommon, the presence of platelet/endothelial cell adhesion molecule in a small cell neoplasm should not in isolation be taken as evidence of h ematopoietic origin. These results further define the utility of CD31 in th e evaluation of human neoplasms.