P-GLYCOPROTEIN EXPRESSION IN OSTEOSARCOMA S

One of the mechanisms by which multidrug resistance is mediated, is th e mdr1 gene product, P-glycooprotein, Immunohistochemistry was perform ed for 63 osteosarcomas of 54 patients to investigate P-glycoprotein e xpression using the monoclonal antibody JSB-1, Most of the patients we re children or adolescents who had received treatment under the framew ork of the Cooperative Osteosarcoma Study Group, In addition P-glycopr otein expression was assayed in five growth plates, Of all cases 68.5 % stained positive for P-glycoprotein. Cases that had received chemoth erapy showed a higher incidence (80.9 %) of positive P-glycoprotein im munostaining than cases that had not received chemotherapy (66.6 %), N o relation could be established between P-glycoprotein expression and the response to chemotherapy, since the majority of P-glycoprotein pos itive biopsies showed a good response in the surgical specimen after c hemotherapy. Furthermore, 42.9% of P-glycoprotein negative biopsies we re classified as non-responders in the later surgical specimen, In add ition to P-glycoprotein expression in osteosarcomas positive immunosta ining was also detected in osteoblasts, osteocytes, osteoclasts as wel l as in some chondroblasts. The results indicate that P-glycoprotein e xpression in osteosarcomas also exists prior to chemotherapy and resem bles the phenotype of normal bone tissue. However, the determination o f P-glycoprotein by using immunohistochemistry in biopsies of osteosar comas cannot predict the response to chemotherapy.