Venetoclax, Carmustine, Etoposide, Cytarabine, and Melphalan Before Stem Cell Transplant in Treating Participants With Relapsed or Refractory Non-Hodgkin Lymphoma

PRIMARY OBJECTIVES: I. Determine the maximum tolerated dose (MTD) of venetoclax that can be safely combined with carmustine, etoposide, cytarabine, and melphalan (BEAM) prior to autologous stem cell transplant which will the recommended phase II dose (RP2D). II. Determine the safety and efficacy of venetoclax as measured by overall response rate (ORR) at day 100, 12-month survival and freedom from relapse (FFR-12). SECONDARY OBJECTIVES: I. Long term effects (progression-free survival \[PFS\] and overall survival \[OS\]) of addition of venetoclax to BEAM. II. Correlation of response and survival with expression of BCL-2, BCL-XL, and MCL-1 as measured by immunohistochemistry (IHC). OUTLINE: This is a dose-escalation study of venetoclax. Participants receive venetoclax orally (PO) once daily (QD) on days -10 to -1, carmustine intravenously (IV) on day -6, etoposide IV twice daily (BID) on days -5 to -2, cytarabine IV BID on days -5 to -2, and melphalan IV on day -1. Participants then undergo hematopoietic stem cell transplantation on day 0. After completion of study treatment, participants are followed up for 2 years.