Effect of P-glycoprotein expression on outcome in the Ewing family of tumors

This study was designed to determine the prognostic significance of multidr ug-resistance, mediated by P-glycoprotein (Pgp) expression, in Ewing sarcom a. The clinical and laboratory features, treatment protocol, and outcome of 75 patients with Ewing sarcoma or peripheral neuroectodermal tumor treated between 1972 and 1997 were reviewed. Pgp expression was tested with the mo noclonal antibody JSB-1. Thirty four (64%) of the 53 tissue samples from un treated patients stained positive for Pgp. Progression-free and overall sur vival were 44 and 59%, respectively, in patients with negative findings, an d 28 and 41% in those with positive findings; neither difference was signif icant. Of the 12 relapsed patients, 6 (50%) expressed more Pgp after chemot herapy than at diagnosis and 4 (33%) expressed less. Within these subgroups , 5 out of 6 and 3 out of 4 died from the disease. No correlation was found between Pgp and known prognostic factors of Ewing tumors. Pgp expression i s probably an intrinsic factor of Ewing tumors but has no correlation to pr ognosis.