Phase 1 study of the histone deacetylase inhibitor entinostat plus clofarabine for poor-risk Philadelphia chromosome-negative (newly diagnosed older adults or adults with relapsed refractory disease) acute lymphoblastic leukemia or biphenotypic leukemia

•The clinical outcome for older adults with ALL or ABL ineligible for multi-agent chemotherapy are poor and are a rare, unmet need.•Entinostat plus clofarabine was well tolerated but infectious and metabolic derangements were more common in the older population (vs younger).•Events of hyperglycemia and peripheral neuropathy were not appreciated with the use of Entinostat plus clofarabine.•Entinostat plus clofarabine appears to be active in older adults with de novo ALL/ABL, and further study of this combination should be considered.