Immunohistochemical evaluation of P‐glycoprotein in human malignancies by monoclonal antibody MC57

P‐glycoprotein expression was analyzed on 137 formalinfixed, paraffin‐embedded human tumours by monoclonal antibody (MAb) MC57. This MAb recognizes an extracellular human specific P‐glycoprotein epitope and defines their multidrug resistance (MDR) phenotype by its binding on cells. Immunohistochemistry indicated that this MAb reacted in human cells and tissues in the same pattern as that found with other MAbs to P‐glycoprotein. However, the present extensive study demonstrated that MAb MC57 is a highly specific reagent for the evaluation of an extracellular P‐glycoprotein epitope preserved after fixation procedures and that this MAb is available to assess P‐glycoprotein expression in routinely processed human tumour specimens. © 1994 Wiley‐Liss, Inc.