Immunohistochemical and ultrastructural investigation of neural differentiation in Ewing sarcoma/PNET of bone and soft tissues

The authors evaluated the role of immunohistochemistry and electron microsc opy tin defining neural differentiation in 28 cases of Ewing sarcoma/PNET. The panel of primary antibodies used included vimentin, MIC-2. NSE. S-100 p rotein, leu7, neurofilaments, GFAP, and chromogranin A. Cases were consider ed undifferentiated when neural markers were absent, poorly differentiated if one neural marker was present, and well differentiated if two or more ma rkers were observed. Cases were also evaluated for the presence of cytoplas mic processes, microtubules, and neurosecretory granules as ultrastructural features of neural differentiation: the tumor was classified as well diffe rentiated if two of these features were present; and poorly differentiated if one was evident; all other cases were considered undifferentiated. Accor ding to immunohistochemistry, 10 cases (35.7%) were undifferentiated, 12 ca ses (42.9%) were poorly differentiated, and 6 (21.4%) were well differentia ted. According to the ultrastructural analysis. 10 tumors were undifferenti ated (35.7%), 14 poorly differentiated (50%), and 4 well differentiated (14 .3%). The overall concordance between the two techniques was low (35.7%). a nd both modalities were concordant in classifying only 1 well-differentiate d, 5 poorly differentiated, and 4 undifferentiated tumors. In conclusion, t he authors suggest that investigations devoted to test the prognostic signi ficance of neural differentiation in these neoplasms should employ both imm unohistochemistry and electron microscopy, separately and in combination, t o assess what is the most effective choice for predicting the clinical cour se.