The impact of pre-existing monoclonal gammopathy on patient outcome in newly diagnosed multiple myeloma

Multiple myeloma (MM) is consistently preceded by monoclonal gammopathy of undetermined significance (MGUS), smoldering myeloma (SMM), or solitary plasmacytoma (SPC). However, there is a lack of data regarding the impact of these pre-existing monoclonal gammopathies (MGs) on MM outcomes.

Gaurav Goyal from the Division of Hematology, Mayo Clinic, Rochester, MN, USA, and his team utilized their institution’s data from 1973 to 2015 to ascertain the impact of prior known MGs on MM outcomes.

Patient population and study design

• Patients with prior diagnosis of MGUS, SMM, or PC from 1973 to 2015 (cases) were identified from the institution’s database and compared to a known MG
• N = 774 patients with a prior diagnosis:
• MGUS (n = 407)
• SMM (n = 232)
• SPC (n = 135)
• A control population (1:2) matched for the year of diagnosis (n = 1548)
• Median follow-up: 81 months
• The primary outcome was overall survival (OS)
• Median OS was calculated using the Kaplan–Meier method and compared using the Log-rank test
• Multivariate analysis was performed to ascertain factors impacting all-cause mortality
• Descriptive statistics were depicted as medians with inter-quartile range (IQR) or frequencies
• The median age at diagnosis of MM: 66 years (IQR 58–72)
• The median age control cohort was 63 years (IQR 55–70)

Key findings

• The cases showed a longer median OS than the controls (71 months vs. 56 months)
• The improved OS was limited to those with a known prior diagnosis of SMM (80 months) and SPC (95 months), compared to MGUS (60 months)
• Multivariable analysis revealed that MM patients with known prior MG had less overall mortality than those without, and this was limited to prior SMM/SPC group (HR 0.68, 95% CI: 0.50–0.93), as compared to the MGUS group (HR 0.83, 95% CI: 0.66–1.05)
• Response to first-line treatment (VGPR) was lower in the patients with known pre-existing MGs as compared to the control group (32% vs. 41%, P = 0.03)

Dr. Goyal and his team determined that MM patients with known pre-existing MGs had superior outcome as when compared to those without. The team identified that patients with prior SMM and SPC diagnosis were associated with improved OS as compared to prior MGUS patients. The research team identified that there is a crucial need for a large prospective screening study of MGUS with a prolonged follow-up period to arrive at appropriate monitoring recommendations.