PROJECT SUMMARY Multiple myeloma (MM) is a malignant plasma cell neoplasm leading to anemia, hypercalcemia, renal insufficiency and bone lesions. It is preceded by a common benign monoclonal plasma cell expansion called monoclonal gammopathy of undetermined significance (MGUS) that shares the same initiating events seen in MM. These include recurrent immunoglobulin gene translocations, and hyperdiploidy. There is a third clinical entity in between these two, smoldering multiple myeloma (SMM), in which there has been more extensive plasma cell expansion than MGUS, but the malignant features of MM are not seen. This project is focused on using genetics to more precisely demarcate benign from malignant plasma cells and develop a patho-genetic definition of MM. We hypothesize that an accumulation of secondary genetic events mark the progression from a benign to malignant state. These events involve a handful of pathways common to many cancers: MYC/MAX, MAPK (NRAS, KRAS, BRAF, FGFR3, PTPN11, NF1), NFKB (TRAF3, TRAF2, CYLD, BIRC2/3, MAPK3K14), TP53/MDM2, RB1/CDKN2C, Others (DIS3, FAM46C). One of these pathways is dysregulated in >95% of MM and <5% of MGUS, and we postulate that individually or in combination they can be used to define malignant plasma cells. There is also increasing evidence of a role of the tumor microenvironment in progression of SMM, and recently clonal hematopoiesis has been associated with increased inflammation, and more rapid progression of MM. We will use next generation sequencing to identify clonal hematopoiesis, and to characterize the genetic events present in patients with MGUS, SMM and MM, and correlate these with the clinical course. We will validate our findings in an independent cohort of patients with SMM enrolled on prospective randomized clinical trials. Ultimately, we hope that a genetic definition will allow both the early detection and prompt treatment of MM, resulting in the prevention of the malignant consequences of MM, and prolonged survival for patients.