QUANTITATIVE IMMUNOCYTOCHEMICAL ASSAYS OF P-GLYCOPROTEIN IN BREAST CARCINOMAS - CORRELATION TO MESSENGER-RNA EXPRESSION AND TO IMMUNOHISTOCHEMICAL PROGNOSTIC INDICATORS

Background: Chemotherapy failure that is due to cellular drug resistan ce remains a major problem in most cancer patients. One type of drug r esistance that has been characterized is the multidrug resistance phen omenon, which demonstrates a reduced ability of cancer cells to accumu late drugs as a result of the effects of an energy-dependent unidirect ional drug efflux pump with a broad substrate specificity. This drug p ump is composed of a 170-kd transmembrane glycoprotein referred to as the P-glycoprotein (P-gp) that uses energy in the form of adenosine tr iphosphate to transport drugs through a channel formed by transmembran e segments. Purpose: Our purpose was fo detect the levels of P-gp expr ession in frozen untreated breast carcinomas by immunocytochemical ass ays and to correlate these levels to current prognostic indicators and , in a few cases, to MDR1 (also known as PGY1) mRNA expression by poly merase chain reaction (PCR). Methods: The immunocytochemical expressio n of the multidrug resistance gene, P-gp, was investigated using a spe cific monoclonal antibody (JSB1) against P-gp in 5-mu m frozen sequent ial sections of breast carcinomas obtained from 213 patients. Microsco pic images of immunostained preparations were evaluated by image analy sis and were compared with MDR1 transcription (mRNA) assessed by PCR i n 16 patients. Quantitative P-gp immunocytochemical assays were correl ated to histoprognostic factors and immunocytochemical indicators. Res ults: Among the 213 breast carcinomas tested, 113 (53%) mere P-gp posi tive, but in 28% of the tumors, the immunostained surface accounted fo r less than 5% of the total area stained. Quantitative immunocytochemi stry reflecting the amount of intracellular P-gp antigen strongly corr elated (r = 0.865; two-sided, P<.0001; Pearson's test) with the quanti tative evaluation of the scanner analysis of mRNA transcripts. The P-g p expression was significantly (two-sided, P<.001) correlated with p53 expression in tumors, to cathepsin D and Ki67 (two-sided, P<.01) immu noreactivity, and to a lesser extent, the detection of estrogen recept or antigenic sites (two-sided, P =.019). P-gp expression was found to be independent of expressions of progesterone receptor and pS2, pHER-2 /neu, and CD31 in tumors and from patient age, tumor size, histologic types, grades and Nottingham prognostic index, and nodal status. Concl usions: The quantitative immunocytochemical assays of P-gp are correla ted to PCR analysis of MDR1 expression, and such correlations can be u seful in evaluating potential multidrug resistance in breast cancer. H owever, the clinical significance of P-gp immunodetections remains to be further determined.