Mivebresib (ABBV-075) is a small molecule Bromodomain and Extra-Terminal motif (BET) inhibitor being studied in a Phase 1 clinical trial in patients with advanced hematologic malignancies and solid tumors. Mivebresib binds to BRD4 with a Ki of 1.5 nM. Comprehensive preclinical characterization of ABBV-075 demonstrated broad activity across cell lines and tumor models, representing a variety of hematologic malignancies and solid tumor indications. In most cancer cell lines derived from solid tumors, ABBV-075 triggers prominent G1 cell-cycle arrest without extensive apoptosis. Consistent with its broad spectrum of activities in vitro, ABBV-075 has comparable or superior efficacies to standard of care agents in flank xenograft mouse models of non-small-cell and small cell lung cancers, pancreatic, breast, prostate, head & neck cancers, multiple myeloma, diffuse large B cell lymphoma and leukemia.