Natural History of Skeletal Related Events in Patients with Multiple Myeloma Who Received First- and Second- Line Therapy with Novel Agents: Results from a Single Center Analysis in 620 Patients

Introduction: Skeletal-related events (SREs) that include pathological fractures, spinal cord compression (SCC) and need for radiotherapy or surgery to the bone are frequent complications of multiple myeloma (MM). Although the incidence of SREs at diagnosis is well-documented, there is limited information for the natural history of SREs during treatment with novel agents. Thus, we evaluated the SRE rate in MM patients who received frontline and second line therapy with proteasome inhibitors (PIs) or immunomodulatory drug (IMiD)-based therapies and explored possible correlations with disease or genetic features and type of treatment.

Methods: MM patients who received frontline therapy in our center (Department of Clinical Therapeutics, University of Athens, Greece), between 2007-2017, were included in this analysis. Patients had a whole-body skeletal survey using either conventional radiography (WBXR) or low-dose CT (WBLDCT) at diagnosis and then at the time of relapse or whenever clinically indicated. Magnetic Resonance Imaging (MRI) of the spine and pelvis at diagnosis was recorded when available. SNPs in genes that are involved in bone destruction in osteoporosis were also evaluated: LRP5 (rs4988321), GC vitamin D (rs4588), TNFRSF11A (rs3018362), DKK1 (rs1569198), RANKL (rs9594759), OPG (rs6469804) and ERS1 (rs1038304).

Results: In total, 620 consecutive patients with symptomatic MM (316M/304F, median age: 65 years) were studied. The median follow-up was 54 months. At diagnosis, osteolytic disease was present in 408 (66%) patients. MRI was available in 390 patients: 149 (38%) patients had focal, 139 (36%) diffuse, 81 (21%) normal and 21 (5%) variegated pattern of marrow involvement. SREs were observed in 271 (44%) patients at diagnosis: 213 (34%) presented with pathological fractures (183 with vertebral fractures, 18 with rib fractures and 15 with long bone fractures; 32 patients had both vertebral and long bone or rib fractures), while 34 (5.5%) patients needed surgery to bone, 45 (7.2%) radiotherapy and 31 (5%) patients presented with SCC. The incidence of SREs was higher in patients with osteolytic lesions (76.4% vs. 12.4%, p<0.0001) or abnormal MRI pattern (49% vs. 11.3%, p<0.0001) at diagnosis. No correlation was found between the presence of SREs at diagnosis and a specific SNP of those studied. Frontline therapy with IMiD-based regimens was given in 38% of patients; 27% patients received bortezomib-based regimens and 28% both IMiD and bortezomib-based therapies (VTD or VRD); 7% received only conventional chemo. Bisphosphonates (BPs) were given to 465 patients (75%) at diagnosis; the vast majority (91%) received zoledronic acid. The remaining 155 patients did not receive upfront BPs, mainly due to renal insufficiency. During first line treatment, 39 (6.3%) patients developed a SRE: 25/341 (7.3%) on bortezomib- (including combos with an IMiD) and 14/235 (6%) on IMiD-based regimens. At the time of first relapse, 4.5% of patients presented with new fractures and 12% required local radiotherapy to bone (SRE rate: 16.5%). The rate of SREs at first progression was much higher in patients who did not receive upfront BPs (92.3% vs. 7.7%). There was no difference in the incidence of SREs at first relapse between patients who received PI- vs. non-PI-based regimens as first line therapy (54.2% vs. 45.8%, p=0.544). During second line therapy, 12.2% of patients developed a SRE, with no difference regarding the second line therapy (PI- or IMiD-based regimens). In total, 126 (20.3%) patients developed at least one SRE, during the course of the first and second line of therapy; this was more common in those who presented with an SRE at diagnosis (33% vs 12%; p<0.03).

Conclusions: Our data, which constitutes one of the few systematic reports on the incidence and characteristics of SREs in the era of novel agents, indicate that SREs remain a significant complication in MM. Despite high response rates after first line therapy and the broad use of BPs, more than 20% of patients develop a new SRE during the first and second line treatment or at the time of first relapse. Importantly, patients who do not receive BPs due to renal impairment develop very frequently SREs, suggesting an unmet need in this setting. More effective frontline therapies or more potent bone-targeted agents (denosumab or anti-sclerostin drugs) may manage to further reduce the SREs rate in MM patients, especially in those who cannot receive BPs.