ESR1 and triple-negative breast carcinoma: Consistent with these observations, luminal ER+PIK3CA-mutant HCI-011 patient-derived breast cancer cells (PDTCs) were sensitive to short-term treatment with GDC-0032, while triple-negative breast cancer (TNBC) PIK3CA wild-type (wt) HCI-001 PDTCs were resistant (Figure 1A).