RecruitingPhase 2ProcedureVenetoclax for the Treatment of Patients With Relapsed Hairy Cell LeukemiaThis phase II trial tests how well venetoclax works in treating patients with hairy cell leukemia that has come back after a period of improvement (relapsed). Venetoclax is in a class of medications called B-cell lymphoma-2 (BCL-2) inhibitors. It may stop the growth of cancer cells by blocking Bcl-2, a protein needed for cancer cell survival.