The study will consist of 2 arms: Arm A and Arm B (if applicable). Arm A dose escalation will investigate up to 3 doses of ABBV-838 at 3-week dosing intervals (Q3W) in combination with venetoclax and dexamethasone. Arm A dose expansion portion will investigate the ABBV-838 Q3W dosing interval with venetoclax and dexamethasone at the recommended phase two dose (RPTD) combination defined from the Dose Escalation portion.~Based on data from the ongoing ABBV-838 monotherapy study (Study M14-467) Arm B dose escalation may be conducted, if deemed necessary. If conducted, Arm B dose excalation will investigate up to 3 doses of ABBV-838 at either weekly (Q1W) or bi-weekly (Q2W) dosing intervals in combination with venetoclax and dexamethasone. Arm B dose expansion portion will investigate either the ABBV-838 Q1W or Q2W dosing interval in combination with venetoclax and dexamethasone at the RPTD combination defined from the Dose Escalation portion.
This is an open-label, multicenter clinical trial designed to evaluate the safety and potential efficacy of venetoclax and ABBV-838 combination therapy with dexamethasone in participants with relapsed or refractory multiple myeloma (MM) who have received 2 or more prior lines of therapy for multiple myeloma (MM). The study will consist of 2 arms: Arm A and Arm B (if applicable). Each arm will have a dose escalation and dose expansion portion.