NSMM can be subclassified into two main categories: [1] oligosecretory myeloma, where M-protein levels are detectable only by highly sensitive methods such as FLC assays or immunofixation, and [2] true NSMM, which lacks detectable immunoglobulin production even by the most sensitive assays [36,40,41]. Here, MYOM2 is linked to plasma cell myeloma.