Real-world outcomes of SLiM-only multiple myeloma: Korean Multicenter Retrospective analysis (KMM2401 study).

In the 2014 update, SLiM biomarkers were included into the "myeloma defining events" as these markers were shown to be significantly associated with early progression to active multiple myeloma (MM). However, several subsequent studies have reported more favorable outcomes. To further clarify the clinical implications, we conducted a retrospective analysis. Patients diagnosed with MM based solely on SLiM biomarkers (SLiM-only MM) 8-17were included. Patients were analyzed according to whether they underwent active observation (group 1) or immediate treatment (group 2). From 2011 to 2023, 72 cases were collected from 8 tertiary institutes in Korea. The median age was 65, and 40 (56%) were male. In terms of the SLiM criteria, 27 patients had bone marrow plasma cell(BMPC) ≥ 60%, 31 patients had serum free light chain ratio (FLCr) ≥ 100, and 35 patients had > 1 focal lesion on MRI. Thirty-five patients were included in group 1, and the median time to progression to MM was 75.8 months. Regardless of the fulfilled SLiM criteria, patients exhibited lower 2-year risk of progression to MM compared with previous studies. Patients with > 1 focal lesion on MRI showed significantly lower 2-year risk of progression than those with BMPC ≥ 60% or FLCr ≥ 100 (p = 0.014). In group 2, the estimated median PFS was 56.8 months. Patients with SLiM-only MM exhibited an extended TTP without treatment compared to prior studies, particularly those with > 1 focal lesions on MRI. In addition, the first-line treatment resulted in favorable outcomes, which may support the benefit of earlier initiation of treatment.