PIK3CA and breast cancer: Consistent with this notion, a recent study indicated that ER+ breast cancer with PIK3CA mutations and reduced survival is associated with amplification at the 11q13-14 locus [12] that harbors USP35. Interestingly, two of the ER+ breast cancer cell lines used in our study, MCF-7 and T-47D, contain hotspot mutations in PI3K, E542K, and H1047R respectively [40].