Risk Factors Associated with Development of Extramedullary Disease in Multiple Myeloma

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