In the present study, SOX2 was upregulated while CD44 was downregulated in dog BC 3D and 2.5D organoids compared with the 2D urothelial carcinoma cell lines (Fig. 3), suggesting that SOX2 is implicated in the progression and proliferation of BC in dogs by increasing the stemness and could be considered as a novel and reliable CSC marker in dog urothelial carcinoma. Here, SOX2 is linked to breast cancer.