Investigation of efficacy of two different chemotherapy protocols used in neoadjuvant chemotherapy in clinical stages II-IV canine malignant mammary tumours

The first aim of this study is to demonstrate the clinical efficacy and reliability of two different neoadjuvant chemotherapy (NAC) protocols consisting of doxorubicin/cyclophosphamide (AC) and paclitaxel in dogs with clinical stages II-IV canine malignant mammary tumours (CMTs). Secondly, to determine the Luminal A, Luminal B, HER2-positive and triple-negative molecular subtypes and their value in predicting clinical response to NAC in biopsy samples, and thirdly, to reveal the changes in Ki-67, human epidermal growth factor receptor type 2 (HER2), oestrogen receptor (ER), and progesterone receptor (PgR) expression levels induced by NAC. Thirty dogs with clinical stages II-IV CMTs (T1-3N0-1M0) according to the modified TNM system were included in the study. Dogs in group-1 (n = 15) AC combination and dogs in group-2 (n = 15) were administered paclitaxel. Partial response (PR) was the most common clinical response in both treatment groups (66.66% and 86.66%, respectively). There was no difference between the groups regarding clinical response parameters (p = .001). The rate of treatment responders was higher than the rate of non-responders in both groups (p < .001). The adverse effects observed in both groups were mostly limited to grades 1 and 2 and all were easy to manage. The most frequently detected molecular subtype was Luminal A (59.25%). Complete response (CR) was achieved in 33.33% of dogs with triple-negative CMT in the AC group and 14.29% of the Luminal A subtype in the paclitaxel group. Alterations in Ki-67, HER2, ER, and PgR expressions after chemotherapy were not statistically significant (p > .05). As a result, we have shown that these neoadjuvant chemotherapy protocols are effective and safe alternative treatment options for CMTs.