Non-secretory multiple myeloma: from biology to clinical management.

Multiple myeloma (MM) is the second most common hematologic malignancy in the US. It is typically characterized by production of large amounts of defective immunoglobulin (Ig). Diagnosing MM and monitoring treatment response, including eventual relapse, are largely based on sequential measurements of Ig. However, a small subset of MM called non-secretory multiple myeloma (NSMM) produces no detectable Ig. This subset of true NSMM has become even smaller over time, as the advent of the serum free light chain assay has resulted in the majority of NSMM patients being recategorized as light-chain MM - that is, MM cells that produce only the light-chain component of Ig. True forms of NSMM, meaning MM that secretes no monoclonal proteins whatsoever, constitute a distinct entity that is reviewed; definition of NSMM using current detection methods, discuss the biology underpinning NSMM development, and share recommendations for how NSMM should be managed clinically with respect to detection, treatment, and monitoring.