Clinical and Diagnostic Challenges in Patients with Concomitant Plasma Cell Disorders and Myeloproliferative Neoplasms

Background:

Monoclonal gammopathy of undetermined significance (MGUS) is a plasma cell precursor disease that regularly precedes the development of multiple myeloma (MM). It accounts for about 4.5% in the entire population, however patients with myeloproliferative neoplasms (MPN) seem at a higher risk for MGUS with a reported rate of concomitant disease at 3-14%. The reason for this co-occurrence of MGUS and MPN remains unclear, and a common cell of origin has not yet been defined. Inversely, constant MPN-driven inflammation in the bone marrow microenvironment (BM) may stimulate the expansion of a pre-existing plasma cell clone thereby promoting the transition from MGUS to active MM. Here, we investigated the clinical and molecular characteristics of a comprehensive series of cases treated for MGUS/MPN overlap at our center.

Methods:

Patients who were diagnosed with concomitant MGUS/MM and MPN between 2006 and 2023 were identified by retrospective chart review, yielding a total of 13 cases.

Results:

We identified 5/13 patients with a confirmed diagnosis of MGUS and 8/13 cases with active MM, all coinciding with a diagnosis of MPN (5 polycythemia vera (PV), 4 chronic myelomonocytic leukemia (CMMol), 3 primary myelofibrosis (PMF), 1 chronic myelogeneous leukemia (CML)). Median age at diagnosis was 66 (range 44-78) years for MGUS/MM and 64 (range 43-81) years for MPN. Overall survival in our cohort was rather short at a median of 8.2 (range 0-16) years. For clinical management, anti-MM therapy was prioritized over MPN treatment in the majority of patients, with the exception of CMMol. MPN-related organ restrictions significantly limited treatment options for MM, including bleeding disorders, infectious complications and impaired hematopoiesis (in PMF). High-dose concepts were performed in transplant-eligible cases, including autologous in 4 and allogenic stem cell transplantation in 2 patients. Two out of 6 patients died under transplant (1 autologous graft failure), indicating a comparably high transplant-related mortality. Another patient died from MM progression as PMF-induced anemia did not allow for more intense treatment.

To examine the evolutionary path from MGUS to MM and the potential impact on this transformation by a concomitant MPN, we next examined the clinical course of disease in each patient. Six out of 13 patients had secondary MPN after prior MGUS/MM diagnosis, 5/13 patients were diagnosed with MPN first, and for 2/13 cases BM assessment revealed coincidental findings of MPN/ MM at the same time. For the cases of secondary MPN after initial diagnosis of MM/MGUS, latency between both diseases was shorter, than vice versa (40.2 vs. 73.6 months, P=0.19). No association was observed between secondary MPN and prior treatment for MM, as only 1/6 patients was diagnosed with PV following high-dose melphalan chemotherapy, potentially pointing towards a negligible role of treatment-induced secondary primary malignancies the context of MM/MPN overlap. In contrast, MGUS progression to active MM was observed in 1 patient with hyperdiploid IgG kappa MM (including trisomy 9) and long-term coexistent JAK2-mutated PV. Another patient was diagnosed with IgG kappa MM and 9p gain along with concomitant JAK2-mutated PMF. Whole-genome sequencing (WGS) is currently ongoing for these patients to decipher the temporal relationship of MM/MGUS and JAK2-mutated MPN.

Conclusions:

The prevalence of MGUS/MM in MPN patients seems modestly increased as compared to the entire population. From a clinical viewpoint, overlap of both diseases poses significant challenges to healthcare providers as treatment-related mortality tends to be higher than in patients with mutually exclusive MPN/ MM. Improved understanding of the molecular interplay of both diseases will inform risk-adjusted treatment decisions and will lead to improved outcomes in this highly challenging subgroup of patients.