Evaluation of Pgp (MDR1) immunohistochemistry in canine lymphoma - prognostic and clinical aspects.

Permeability glycoprotein (P-glycoprotein, Pgp) immunohistochemistry (IHC) was evaluated in dogs with multicentric lymphoma treated with cyclophosphamide- doxorubicin-vincristine-prednisolone with or without L-Asparaginase. Lymph nodes of 33 untreated dogs were immunophenotyped: Ki67% and Pgp analyses (with anti-Pgp, monoclonal mouse C494 clone) were performed. Pgp positivity rate and intensity were determined microscopically (by manual counting done by two blinded authors in two parallel specimens). The median overall survival time (OST) was 333 days and the relapse-free period (RFP) 134 days. Pgp expressions were positive in 18 out of 33 (54.5%) of tumour cells. T-cell types stained more intensively. Lower OST and RFP were found with Pgp positivity ≥ 35% (OST: 240 days, RFP: 95 days) compared to Pgp positivity < 35% (OST: 428 days, RFP: 232 days). Intensive staining was associated with a lower OST and RFP (240 and 103 days, respectively) than weak staining (428 and 221 days, respectively). Death due to adverse drug reactions was best predicted at Pgp positivity ≤ 6.5% (sensitivity/specificity: 0.55/0.81) and ≤ 123 days (sensitivity/ specificity: 0.55/0.86). Pgp evaluation by IHC can have prognostic value with a properly established Pgp% positivity cut-off value in dogs treated with Pgp substrate drugs.