PTEN and breast cancer: However, PTEN‐null triple‐negative human breast cancer (TNBC) cells, the main focus of our study, do not express appreciable levels of p110δ, as shown by comparing expression levels of the genes encoding p110 isoforms in these cells and in B‐cell acute lymphoblastic leukemia lines (Fig EV1B, https://portals.broadinstitute.org/ccle), that express all p110 isoforms (Thorpe et al, 2015).