I think it's important to run any decision to use OTC medications or supplements by your PCP AND hem/onc physicians. I am fortunate that there is also a PharmD attached to my PCP's clinic who went through all of my current medications and ruled out any potential complications posed by the addition of curcumin to my regimen. I am not otherwise immunocompromised so I have taken 2000 MG of curcumin daily for nearly a year and a half now with good results and no apparent side effects.

Curcumin is an anti inflammatory substance. Anti inflammatory substances are viewed as anathema by MM and also other cancers. That said, it is controversial and if you decide to take it, consult with a MM oncologist/hematologist - not a pcp and not a "general" oncologist/hematologist. I have read about many issues but have also read positive stories about this substance. The stories were enough to make me think NO but others view it differently.
I have MGUS (IgG lambda); it was diagnosed when I was 59 years old - 23 years ago. My dad had IgA Kappa SMM so I knew what this was about and I was frightened. I think my MM hematologist was also frightened. He ordered blood tests every three months for 17 years - at that time he retired and my6 current MM specialist is not as concerned. I take celebrex and a statin drug (zocor). I have taken zocor since I was 52 years old (although I did not have elevated lipids - long story) and have taken celebrex since 2006-7 (an anti inflammatory) and have never had issues with each. Both drugs are being studied because some investigators believe they can be repurposed for MM. Statins interfere with a rate limiting step for MM and Celebrex is an anti inflammatory. There have been large VA patient studies using statins, which were positive - the conclusion was that patients that took statins had lower rates of progression. Mayo (RST) and the Cleveland Clinic had a clinical trial with celebrex, MGUS and SMM. The doses, however, were low and the results were null. There have also been studies with analogues of Celebrex.
This is a long answer to your question. Again, my advice is to approach Curcumin carefully and get good information to make a decision.