PIK3CA and breast carcinoma: This may offer a mechanistic underpinning for the phenotypic heterogeneity found in PIK3CA-driven breast cancer models (Hanker et al, 2013; Koren et al, 2015; Van Keymeulen et al, 2015) as well as in benign but highly debilitating human PROS disorders (Madsen et al, 2018).