Iberdomide, Daratumumab, Carfilzomib, and Dexamethasone (Iber-KDd) in Patients With Relapsed/Refractory Multiple Myeloma

Participants will receive Iberdomide (Iber) therapy orally (PO) in capsules as follows: * Combination therapy: Cycles 1 to 8: 1 mg per day\*, Days 1 to 21 every 28 days. * Monotherapy: Cycles 9 to 20: 1 mg per day\*, Days 1 to 21 every 28 days. (\*) The first 6 patients will begin at 1 mg/day as lead-in with option to increase to 1.3 mg with dose-escalation cohort after two (2) cycles tolerated therapy

Participants will receive Carfilzomib (K) therapy intravenously (IV) as follows: * Cycle 1: 20 mg/m2 per dose on Day 1; 56 mg/m2 per dose on Days 8 and 15 * Cycles 2 to 8: 56 mg/m2 per dose on Days 1, 8, and 15.

Participants will receive Daratumumab (D) therapy subcutaneously (SC) or intravenously (IV) as follows: * Cycles 1 and 2: 1800 mg SC or 16 mg/kg IV on Days 1, 8, 15, and 22 * Cycles 3 through 6: 1800 mg SC or 16 mg/kg IV on Days 1 and 15 * Cycles 7 and 8: 1800 mg SC or 16 mg/kg IV on Day 1.

Participants will receive Dexamethasone (d) therapy either orally (PO) or intravenously (IV) as follows: * Cycles 1 and 2: 40 mg/dose on Days 1, 8, and 15; 20 mg/dose on Day 22 * Cycles 3 and 4: 40 mg/dose on Days 1, 8, and 15 * Cycles 5 through 8: 20 mg/dose on Days 1, 8, and 15.

Participants will receive Acetaminophen orally (PO) prior to Iber-KDd therapy as follows: * Cycles 1 and 2: 650 mg/dose on Days 1, 8, 15, and 22 * Cycles 3 through 6: 650 mg/dose on Days 1 and 15 * Cycles 7 and 8: 650 mg/dose on Day 1.

Participants will receive Diphenhydramine either orally (PO) or intravenously (IV) prior to Iber-KDd therapy as follows: * Cycles 1 and 2: 25 mg/dose on Days 1, 8, 15, and 22 * Cycles 3 through 6: 25 mg/dose on Days 1 and 15 * Cycles 7 and 8: 25 mg/dose on Day 1.

Participants will receive Montelukast orally (PO) prior to Iber-KDd as follows: * Cycle 1 only: 10 mg/dose, Days 1, 8, 15, and 22, to be administered prior to the first 4 doses of Daratumumab (D).