Immunohistochemical analysis of CD99 and PAX8 in a series of 15 molecularly confirmed cases of Ewing´s sarcoma/PNET family of tumours

ABSTRACT Ewing Sarcoma´s / PNET family of tumours are an uncommon group of malignant neoplasms. A multidisciplinary approach is highly recommended to reach a correct diagnosis, considering the clinical, radiological and histopathological aspects. Since in up to 90% of cases the translocation t (11; 22) (q24; q12) occurs resulting in a chimeric fusion transcript EWSR1-FLI-1. The pathologist has several tools in addition to conventional techniques (hematoxylin and eosin), such as immunohistochemistry, which plays a very important role in the differential diagnosis. We present a series of 15 cases of molecularly confirmed Ewing's sarcoma´s / PNET family of tumours, in which we found a sensitivity of 100% for CD99 and 80% for PAX8 by immunohistochemistry. This indicates a high sensitivity; however, it is known that both CD99 and PAX8 are also expressed in other tumours. Therefore, the molecular confirmation should be performed in all cases.