Risk Factors Associated with Development of Extramedullary Disease in Multiple Myeloma
Authors: Stork Martin , Sevcikova Sabina , Krejci Marta , Adam Zdenek , Sandecka Viera , Maisnar Vladimir , Radocha Jakub , Spicka Ivan , Straub Jan , Minarik Jiri , Pika Tomas , Jungova Alexandra , Gregora Evzen , Pavlicek Petr , Vrabel David , Jarkovsky Jiri , Brozova Lucie , Jelinek Tomas , Hajek Roman , Pour Ludek 
Published: October 2019

Abstract
Background Multiple myeloma (MM) is the second most common hematological malignancy characterized by plasma cell (PC) infiltration of the bone marrow. Unfortunately, better imaging techniques convey multiple reports about increased incidence of the so-called extramedullary disease of MM (EM), an aggressive, mostly resistant entity with poor prognosis for patients. EM probably develops because of 'bone marrow escape' of PC subclone that migrates out of the BM infiltrating soft tissues losing dependence on the BM microenvironment, either partially or completely. There are two types of EM - primary, found at the time of MM diagnosis, and secondary, found at the time of MM relapse. However, there are very few reports about EM.
Aims This study aims to analyze risk factors connected to EM development.
Methods Data from the Registry of Monoclonal Gammopathies (RMG) were analyzed. The RMG represents a database for collection of clinical data concerning diagnosis, treatment and follow-up of Czech MM and other monoclonal gammopathies patients. In total, data of 4985 MM patients were collected into the RMG database between 2007 and June 2017. Our analysis compared patients who developed EM at initiation of first or higher line of therapy with patients without EM during at least 5-year-long follow-up (patients who died earlier included). Logistic regression analysis was used to assess the association of baseline characteristics at MM diagnosis with EM occurrence at first line and relapse, respectively.
Results In total, 4985 MM patients data were collected into the RMG database between 2007 and 2017. Patients were treated with bortezomib, lenalidomide, thalidomide, pomalidomide, ixazomib and daratumumab. Regardless of treatment, EM patients responded worse than MM patients did to any form of treatment. While primary EM patients had similar PFS as MM patients, OS was significantly worse (48.7 vs 60.6 months, resp.). Secondary EM patients did even worse, with PFS 8.7 months and OS 23.8 months only. We found 543 MM patients (10.9%) who developed EM during the entire follow-up. Out of these EM patients, we found 309 patients who were diagnosed with primary EM at initiation of first line of therapy. At initiation of 2nd line of treatment, we found 111 secondary EM patients. At 3rd, 4th and 5th, we found 61, 39 and 23 EM patients, resp. Finally, 309 patients who developed EM at initiation of 1st line and 234 patients who developed EM at initiation of further treatments were compared to 2092 patients who did not develop EM during the entire course of the disease. Overall, occurrence of EM at 1st or higher lines of treatment was associated with younger age, male sex, low ISS, D-S substage A, low B2 microglobulin, low creatinine, high hemoglobin, elevated thrombocytes, other types of M-Ig than IgG and presence of bone lesions. For EM cases found only at initiation of 1st line (primary EM), we found association with high ECOG status, low LDH, low M-protein quantity and low % of plasma cells infiltration in the bone marrow. For EM cases found at MM relapse (secondary EM), we found association with high D-S stage, high LDH, high CRP, high Ca, del13q and gain1q.
Conclusion EM remains an aggressive disease with poor prognosis regardless of use of novel drugs. Surprisingly, in our group of patients, most EM disease developed early in the course of the disease - more than 60% at first relapse. We analyzed risk factors connected to development of EM and found that LDH, hemoglobin, thrombocytes and M-Ig status were associated with EM development. We suggest that in such patients, PET/CT or whole body MRI should be performed regularly to ensure early detection of EM.
Grant support: AZV 17-29343A.

Disclosures
Maisnar: BMS: Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Hajek:Amgen: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding.