Classifications of Multiple Myeloma

Myeloma can be discovered at a precancerous stage. In some cases, the myeloma cells build up very slowly in the bone marrow.

The very earliest stage is called Monoclonal Gammopathy of Undetermined Significance (MGUS). This is not a cancer. In MGUS, the myeloma cells constitute fewer than 10% of the bone marrow cells. The risk of transition from MGUS to active myeloma is very low: only a 1% chance each year of follow-up. 

Even if the myeloma cells are at a higher level of 10%–30% of the total bone marrow, the growth rate can be very slow and represent asymptomatic or smoldering multiple myeloma (SMM). 

Both MGUS and SMM can change very slowly over a period of years and do not require active treatment. It is very important to establish the correct diagnosis distinguishing MGUS and SMM from active or symptomatic myeloma, which does require treatment. 

Multiple Myeloma criteria was updated by IMWG in 2014.  

Clonal bone marrow ≥ 10% or bony/extramedullary plasmacytoma AND any one or more of the CRAB criteria or Myeloma Defining Events (MDE) 

Common myeloma symptoms-- “CRAB” criteria are the result of myeloma cells.  Myeloma cells divide and crowd out normal cells in the bone marrow resulting in anemia and reduced immunce system function. They activate cells that destroy bone resulting in bone damage and high blood calcium. If the myeloma cells make antibodies (or parts of antibodies) that are secreted into the blood then they can be filtered out in the kidneys that together with high calcium can contribute to renal complications.