(PA-375) Real-world Outcomes of SLiM-only Multiple Myeloma: Korean Multicenter Retrospective Analysis

In 2014, the IMWG included SLiM biomarkers (BMPC ≥ 60%, FLC ratio ≥ 100, > 1 focal MRI ≥ 5mm) into the "myeloma defining events" because they are significantly associated with early progression to active multiple myeloma. However, several subsequent reports demonstrated that patients who met only SLiM biomarkers (SLiM-only MM) showed favorable outcomes compared to the previous reports. Moreover, there have been no subsequent report dealing with patients with > 1 focal MRI lesions. To further elucidate their clinical impact, we carried out a nationwide retrospective analysis.

Methods:   

Patients who were diagnosed with MM based on only SLiM biomarkers were included in the analysis. Patients with CRAB features, extramedullary plasmacytoma, solitary plasmacytoma, AL amyloidosis, or plasma cell leukemia were excluded. Baseline characteristics, treatment, and outcomes were retrospectively collected. High-risk cytogenetics were defined by the presence of t(4;14), t(14;16), del(17p), and +1q.

Results:   

From 2011 to 2023, 72 cases were collected from 7 tertiary institutes in Korea. The median age was 65 (range, 36 – 89), and 40 (56%) were male. In terms of the SLiM criteria, 27 patients had BMPC ≥ 60%, 29 patients had FLC ratio ≥ 100, and 34 patients had > 1 focal lesion. Twelve (17%) and seven (10%) patients were ISS-III and R-ISS-III, respectively. Nineteen patients (26%) had at least one high-risk cytogenetics. Thirty-five patients (49%) patients were managed with active surveillance (group 1), while the other thirty-seven patients (51%) received immediate treatment (group 2).

In group 1, the median time to progress to CRAB-MM (TTP) was 75.8 months. Patients with > 1 focal MRI lesions only showed significantly prolonged TTP compared to those with BMPC ≥ 60% or FLC ratio ≥ 100 (p = 0.035). With 10 patients (29%) progressed to CRAB-MM, their median TTP was 22.6 months (95% CI, 14.4 – 30.8). Younger patients (≤ 65) were associated with progression to CRAB-MM (p = 0.046), but other prognostic factors including stage, cytogenetics were not associated with TTP, probably due to small number of patients. In group 2, responses by the first-line treatment were as follows: CR 60%, VGPR 8%, PR 22%. PFS by the first-line treatment was 56.8 months (95% CI, 21.2 – 92.4).

Conclusions:   

In the current study, patients diagnosed with SLiM-only MM exhibited an extended TTP without treatment compared to prior studies, particularly those with only focal MRI lesions. In addition, the first-line treatment resulted in favorable outcomes, which may support the benefit of earlier initiation of treatment for SLiM-only MM.