PTEN and breast cancer: The HER2 receptor is an activator of the PIK3CA-Akt and RAS dependent pathways and hence though our data does not demonstrate genetic duplication of the HER2 gene in canine mammary tumors, oncogenic pathways downstream of membranous receptor tyrosine kinases such as HER2 are activated as evidenced by PIK3CA and KRAS activating mutations and PTEN and KRAS copy number alterations (Fig. 2)24,25.