PTEN and breast cancer: In the study by Perren A. et al., loss of phosphatase and tensin homolog (PTEN), an inhibitor of the PI3K/AKT/mTORC1 axis, was correlated with the loss of both ERα and PgR expressions in primary BC specimens (Figure 1), while Garcia J.M. et al. showed that LOH of the PTEN gene, which occurs in approximately 30–40% of sporadic BCs, is associated with a higher tumor histologic grade and loss of PgR, but not of ERα expression [42,43].