P-GLYCOPROTEIN - THE INTERMEDIATE END-POINT OF DRUG RESPONSE TO INDUCTION CHEMOTHERAPY IN LOCALLY ADVANCED BREAST-CANCER

Expression and clinical relevance of p-glycoprotein (p-gp) were evalua ted in 31 cases of locally advanced breast cancer and 9 cases involvin g inflammatory breast cancer after induction chemotherapy. The de novo p-gp expression rate was 26% and increased up to 58% (p = 0.03) with the FAC (5-fluorouracil, adriamycin, cyclophosphamide) regimen. Althou gh more clinically complete responders were found in the secondary p-g p negative group (p = 0.02), this difference was not found in patholog ical tumor response. Moreover, as the grade of the secondary p-gp expr ession increased, the chemotherapeutic effect decreased, suggesting an inverse relationship between p-gp expression and drug effect (p = 0.0 4). When we subgrouped the patients into 4 groups using these two para meters, p-gp negative patients presenting with a high drug effect show ed a low recurrence rate (p = 0.05) and marginal survival benefits (p = 0.09) as opposed to patients with a low drug effect. But in p-gp pos itive groups, the recurrence rate was the same between the two groups regardless of the drug effect. Thus, in the p-gp negative patient with a high drug effect, adjuvant chemotherapy with the same regimen as in duction chemotherapy may induce more prognostically favorable results. Therefore, clinical application of the secondary p-gp detection can b e used as an intermediate endpoint in evaluating drug response for an induction regimen.