TDK conference 2020

Mammary gland tumors are one of the most common malignancies in dogs. First line treatment is usually surgical excision; however, chemotherapy might be also needed. The efficacy of chemotherapeutic agents is often influenced by the emergence of multidrug resistance (MDR) commonly caused by P-glycoprotein (Pgp), a member of the ATP-binding cassette transporter family. The detection of the pump activities in the cellular membranes can be measured by functional tests.

The aim of our study was to determine whether flow cytometry can be used for screening chemotherapy resistance in canine mammary gland tumors, and the results can have prognostic value or not.

Pgp activity was investigated in samples of 35 dogs with mammary tumors by calcein assay. This method uses a fluorescent dye (Calcein-AM) to measure Pgp activity by flow cytometer. Multidrug resistance activity factor (MAF) was derived from the difference of calcein-positive and calcein-negative cells. Control samples originating from the intact mammary tissue of the same animal were compared with the tumorous lesions. Other characteristics (e.g. age, body weight, etc) were also considered in the two groups.

MAF value was found to be significantly higher in mammary tumor cells in comparison with control samples (p=0,0022). The proportion of calcein-positive cells (without efflux pump) was typically higher (median 95.5%) in healthy tissue than in tumor cells (median 81.5%), and the percentage of calcein-negative cells (with efflux pumps) was much lower in control samples compared to tumor samples (median 28.35% vs. 47%, p = 0.0381). Studying benign and malignant groups according to the tumor, significantly lower average age (9 years, p = 0.0397), smaller tumor size (1.75 cm, p= 0.0261) and lower stage (mean 1, p = 0.0008) was found in the first group in contrast to data of patients with malignancies (mean age 11 years, tumor size 2.9 cm, stage 3).

Based on our results significant differences were found between the healthy control samples and the tumour samples using the fluorescence-based technique. Regarding MAF as a prognostic factor, however, further investigation is needed.