ESR1 and breast carcinoma: In fact, Mcl-1 expression levels correlated inversely with sensitivity to ABT-263 in untreated ERα+ breast cancer cells12. Interestingly, Mcl-1 levels were elevated in HCC1428-LTED, MCF7-LTED, and T47D-LTED cells as compared to parental counterparts (Fig. 2a).