Characterization of smoldering multiple myeloma: A population-based cohort study.

e20028 Background: There is increasing interest in characterizing Smoldering Multiple Myeloma (SMM) due to the availability of novel therapies shown to delay symptomatic progression to Multiple Myeloma (MM) with considerably less toxicity. The lack of population-based disease registries has made epidemiologic data on SMM difficult to acquire. Existing cohort studies of SMM patients have largely been conducted in specialized referral centers. This surveillance study characterizes the epidemiology of SMM in a real-world, clinical population using data from a large, integrated healthcare delivery system. Methods: We performed a retrospective study of all new SMM cases identified in Kaiser Permanente Northern California (KPNC) during 2010-2017, based on either (or (2) a new MM diagnosis in the KPNC Cancer Registry without initiation of plasma cell-directed therapy within 1 year of diagnosis. Those without KPNC membership for at least 1 year after diagnosis were excluded. Age at diagnosis, sex, race/ethnicity, and Charlson Comorbidity Index (CCI) at diagnosis were examined. The incidence of SMM was calculated using KPNC membership denominators, and a 2-sided Cochran-Armitage test was used to test for trend. Among the SMM cohort, characteristics were examined using the chi-squared test, including data before/after the Nov 2014 International Myeloma Working Group (IMWG) diagnostic criteria update. Results: A total of 251 new SMM cases were identified from 2010-2017. The average annual incidence of SMM was 1.2 per 100,000, increasing from 1.0 per 100,000 in 2010 to 1.5 per 100,000 in 2017 (p<0.05 for trend). The demographic characteristics of the SMM cohort were notable for mean age 70.0 ± 11.7 years, 63.8% male, and 61.0% non-Hispanic White, 17.1% Black, 10.0% Hispanic, and 11.6% Asian. Overall, 73.7% had at least 1 comorbidity, based on CCI. When comparing 116 SMM cases diagnosed after the IMWG update to 135 cases diagnosed before the IMWG update, those diagnosed after the revised IMWG guidelines were significantly more likely to have at least 1 existing comorbidity (80.2% vs 68.2%, p=0.03). Conclusion We identified a contemporary cohort of patients with SMM from a large, integrated healthcare system. During our 8-year study period, the annual incidence of SMM increased slightly, including after 2014 when the IMWG criteria for SMM were refined. We observed that patients diagnosed after the 2014 IMWG update were more likely to have at least 1 comorbidity. Whether these trends relate to background population characteristics or are specific to recognized SMM cases bears further study. Follow-up analyses will examine the rate of progression from SMM to MM and the presence or absence of severe, irreversible, end-organ damage at the time of progression.