[Multiple myeloma with coexistence of IGH::FGFR3 and IGH::CCND1: two cases report and literature review].

We retrospectively analyzed the clinical data and clonal architecture of two multiple myeloma (MM) patients harboring concurrent IGH::FGFR3 and IGH::CCND1 fusions, with a review of relevant literature. Fluorescence in situ hybridization (FISH) confirmed biallelic IGH translocations in both cases. Case 1, diagnosed with smoldering MM (SMM), exhibited co-positivity for both IGH translocations in 91% of bone marrow plasma cells. Case 2, with active MM, showed predominant IGH::FGFR3 positivity (93% of cells), with a minor subclone (5%) co-expressing IGH::CCND1. This study demonstrates that primary biallelic IGH translocations can lead to the coexistence of IGH::FGFR3 and IGH::CCND1, revealing a novel genetic mechanism driven by biallelic IGH translocations in the founding clone. Furthermore, it elucidates the clonal heterogeneity in biallelic IGH translocation events.