Although mutations in many genes, such as in BRCA1, BRCA2, and TP53 (Markkanen, 2019; Beetch et al., 2020), as well as changes in several mammary cancer-related pathways, such as KRAS, PTEN, and MAPK (Bulkowska et al., 2017), have already been described for both species, the genetic influence in the genesis and development of this tumor and information about epigenetic alterations in canine mammary cancer are still scarcely known. Here, PTEN is linked to breast cancer.