ESR1 and breast cancer: We next investigated whether SRC inhibition would sensitize TRAIL-resistant cells to TRAIL by testing the combination of TRAIL ± PP2 on a panel of breast cancer cell lines representing ER-positive (T47D or MCF7), HER2 amplified (SKBR3, BT474, HCC1954, MB453), TNBC/basal A (HCC1937, BT20, MB468), and TNBC/basal B (MB231, MB157, Hs578t) subtypes (Figure 6E).