Mast cell tumors (MCTs) are the most common tumors in dogs, accounting for 16-21% of cutaneous tumors. Although several small molecule inhibitors, including imatinib mesylate, have been used for the treatment of MCTs, the response rate remains less than 50%. In this study, the effects of different selective signal inhibitors on MCT cell growth were evaluated using 4 different cell lines derived from dogs. We found that the phosphoinositide 3-kinase (PI3K) signaling pathway is crucial for the proliferation of MCT cells in the presence or absence of c-kit gene mutations. Here, we propose a novel therapeutic strategy to target the PI3K pathway for the treatment of canine MCTs.