Chemoresistance markers PGP and BCRP in canine inflammatory and grade 3 mammary carcinoma

Introduction: Multidrug resistance of neoplastic cells is frequently related to the expression of P-glycoprotein (PGP) and breast cancer resistance protein (BCRP). Canine inflammatory mammary carcinoma (IC) and grade 3 carcinoma (C3) are biologically aggressive and they could benefit from chemotherapy. Our study describes the expression of PGP and BCRP in these tumours. Materials and Methods: Samples included 18 C3s and 20 ICs from dogs that had not received chemotherapy before biopsy. Primary carcinoma was identified in 15 cases of IC. Tumours were classified into histological subtypes. IHC for PGP and BCRP was considered positive when O20% and O10% of cells were labelled for PGP and BCRP, respectively. Results: Immunolabelling was mainly membranous for PGP, showing a strong reaction in emboli, while membranous and cytoplasmic labelling was mainly seen for BCRP. PGP was highly expressed in the different tumours, but was significantly higher in emboli of IC versus C3 (PGP P 5 0.006) and in primary IC versus C3 (PGP P 5 0.032). There was no significant difference in BCRP expression between groups, being expressed in 78.95% of emboli of CI, 80% of primary IC and 66.67% of C3. Conclusions: Chemoresistance is a phenomenon present in dogs with C3 and IC. Our results indicate the need for a combined therapy rather than chemotherapy alone. The high expression of PGP in ICs compared with non-inflammatory mammary carcinomas is an interesting finding that can explain a higher resistance to chemotherapy in this type of cancer and could be related to the specific pathogenic mechanisms that this disease exhibits.