[P-glycoprotein expression in osteosarcoma].

One of the mechanisms by which multidrug resistance is mediated, is the mdr1 gene product, P-glycooprotein. Immunohistochemistry was performed for 63 osteosarcomas of 54 patients to investigate P-glycoprotein expression using the monoclonal antibody JSB-1. Most of the patients were children or adolescents who had received treatment under the framework of the Cooperative Osteosarcoma Study Group. In addition P-glycoprotein expression was assayed in five growth plates. Of all cases 68.5% stained positive for P-glycoprotein. Cases that had received chemotherapy showed a higher incidence (80.9%) of positive P-glycoprotein immunostaining than cases that had not received chemotherapy (66.6%). No relation could be established between P-glycoprotein expression and the response to chemotherapy, since the majority of P-glycoprotein positive biopsies showed a good response in the surgical specimen after chemotherapy. Furthermore, 42.9% of P-glycoprotein negative biopsies were classified as non-responders in the later surgical specimen. In addition to P-glycoprotein expression in osteosarcomas positive immunostaining was also detected in osteoblasts, osteocytes, osteoclasts as well as in some chondroblasts. The results indicate that P-glycoprotein expression in osteosarcomas also exists prior to chemotherapy and resembles the phenotype of normal bone tissue. However, the determination of P-glycoprotein by using immunohistochemistry in biopsies of osteosarcomas cannot predict the response to chemotherapy.