Study Comparing Therapy for Advanced Relapsed/Refractory Multiple Myeloma With and Without Dexamethasone

"ICARIA schema :~40mg (20mg for ≥75yr) on day 1, 8, 15, 22 of each cycle plus~IKEMA schema :~20 mg on day 1-2, day 8-9, day 15-16 and day 22-23 of each cycle~For subjects older than 75 years or underweight (BMI \<18.5), the dexamethasone dose may be administered at a total dose of 20 mg weekly.~In both schema (ICARIA or IKEMA), dexamethasone will be administrated up to 2 cycle (Arm 1) or until disease progression (Arm2)"