Abstract:
Multiple myeloma (MM) is a relatively frequent type of hematological malignancy that consists of proliferation of abnormal plasma cells in the bone marrow. MGUS and SMM are asymptomatic precursor conditions that can potentially transition to multiple myeloma. Previous reports indicated that initiating events, such as hyperdiploidy and high-risk translocations including t(4;14), as well as progression drivers—including MAPK pathway mutations (KRAS, NRAS, or BRAF), the inactivation of TP53 or ATM, and the APOBEC mutational signature—are associated with the transformation of precursor lesions to aggressive multiple myeloma. There are few studies investigating diagnosis or prognosis associated-mutations in a longitudal mannner for identification of non-invasive biomarkers. In this study, 76 MGUS and 61 SMM cases were prospectively enrolled, and followed up for 8 years.
During this time period, one MGUS (1.3%) and 5 SMM (8.2%) cases transformed to overt MM. Peripheral blood samples were collected to isolate plasma cfDNA and granulocyte gDNA samples, as well as bone marrow (BM) samples to obtain tumor tissue DNA. cfDNA samples were obtained by seperating plasma through centrifugation of peripheral blood samples, followed by purification of cfDNA with a cfDNA isolation kit. Plasma cells were enriched with FACS by sorting CD138+/CD38+ BM cells from SMM and MM cases, and CD138+/CD38+/CD56+/CD19- populations from MGUS cases. A targeted ultradeep next generation sequencing (NGS) platform including 261 genes known to be recurrently mutated in PCNs was employed to identify somatic mutations in bone marrow tumor tissue DNA and plasma cfDNA samples of MGUS, SMM during diagnosis as well as after transformation to MM. A strict computational analytical pipeline including MuTect2 was used to identify somatic variants, which included variants in BM tumor DNA or cfDNA with % of VAFs more than 4 fold of that of patient-matched granulocyte gDNA. Importantly, 8 of 21 (38%) MGUS cases, 18 of 23 (78.3 %) SMM cases, and 5 of 6 (83.3%) MM cases harbored at least one somatic mutation in plasma cfDNA samples. Among cases that transformed to MM, one of one (100%) MGUS and 4 of 5 (80%) SMM cases harbored somatic mutation(s) in cfDNA whereas non-transformed cases had mutations in 7 of 20 (35%) MGUS and 14 of 18 (77.8%) SMM cases.
In general, the numbers of point mutations and indels were higher in bone marrow tumor DNA samples compared with those of plasma cfDNA samples. Importantly, most of the somatic mutations identified in plasma cfDNA samples of MGUS (86.5%), SMM (100%) or MM (87.5%) were also present in patient-matched BM tumor DNAs. Some of these were already known, potentially oncogenic mutations such as those of BRAF or MAX genes. Certain COSMIC annotated mutations in genes like KMT2C were present in patient-matched pre- and post-transformation cfDNA and BM tDNA samples. Our observations were generally in accordance with a previous study by Bustorus et al. JCO 2020 suggesting the presence of driver mutations at the SMM stage. Different than the findings of a recent report by Samur et al. JCO 2026, we did not observe difference in somation mutation numbers between transformed and non-transformed cases. In conclusion, targeted ultra-deep sequencing may enable the non-invasive identification of somatic mutations in MGUS or SMM cases with the potential to progress to MM. Furthermore, the identification of oncogenic mutations may help guide patient-specific targeted therapies.
