Phase I dose escalation of H3B-6545, a first-in-class highly Selective ERα Covalent Antagonist (SERCA), in women with ER-positive, HER2-negative breast cancer (HR+ BC).

1059Background: H3B-6545 inactivates both wild-type and mutant ERα by targeting cysteine 530 and enforcing a unique antagonist conformation. Methods: Women with locally advanced or metastatic HR+ B...