PIK3CA and breast neoplasm: We observed a similar sensitivity in a pair of mouse breast tumor cell lines (MycOE Pik3ca Mut and MycOE Pten Null) and an isogenic pair of PTEN WT and PTEN−/− HCT116 cell lines (55), in which the PTEN Null cells were more sensitive to transcription inhibition than the PTEN WT cells (Figure 5C–F; middle and right), implying that PTEN loss sensitizes cells to transcription inhibition.