Light-chain (LC) monoclonal gammopathy of undetermined significance (MGUS) is a precursor of multiple myeloma (MM) and related conditions. LC-MGUS is characterized by free light-chain (FLC) levels outside defined reference intervals, indirectly indicating underlying plasma cell (PC) monoclonality. Next-generation flow cytometry (NGF) was used to evaluate clonal PC presence in bone marrow (BM) samples from individuals with LC-MGUS in the iStopMM study, aiming to assess the predictive value of the FLC ratio for clonal PC presence and its prognostic implications. BM samples from 61 individuals with LC monoclonal gammopathy were analyzed. Clonal plasma cells were detected in 53.6% of LC-MGUS samples (n = 28) and in all samples from individuals with more advanced conditions (n = 33). The FLC ratio was predictive of clonal PC presence for kappa-involved FLC ratios (p < 0.05; n = 42), with an optimal cutoff of 3.15 (96.7% sensitivity, 91.7% specificity). Of 195 individuals with kappa-involved LC-MGUS in follow-up within the iStopMM study, none with FLC ratios >1.65 to 3.15 progressed to MM (n = 124), whereas 4/71 (5.6%) with FLC ratios >3.15 progressed over median follow-up of 55 months. These findings support using a kappa-involved FLC ratio cutoff of >3.15 to more accurately identify individuals at increased risk of developing symptomatic PC disorders.
轻链型意义未明单克隆丙种球蛋白病（LC-MGUS）是多发性骨髓瘤（MM）及相关疾病的前期病变。LC-MGUS的特征是游离轻链（FLC）水平超出既定参考范围，间接提示潜在的浆细胞（PC）单克隆性。在iStopMM研究中，采用新一代流式细胞术（NGF）检测了LC-MGUS个体骨髓样本中的克隆性浆细胞，旨在评估FLC比率对克隆性浆细胞存在的预测价值及其预后意义。研究对61例轻链型单克隆丙种球蛋白病患者的骨髓样本进行了分析。结果显示，53.6%的LC-MGUS样本（n=28）检测到克隆性浆细胞，而在所有病情更晚期的个体样本（n=33）中均检出克隆性浆细胞。对于κ轻链型FLC比率，其数值能预测克隆性浆细胞的存在（p<0.05；n=42），最佳临界值为3.15（敏感性96.7%，特异性91.7%）。在iStopMM研究随访的195例κ轻链型LC-MGUS个体中，FLC比率>1.65至3.15的患者（n=124）无一进展为多发性骨髓瘤，而FLC比率>3.15的患者中，有4/71例（5.6%）在中位随访55个月内发生进展。这些研究结果支持采用>3.15的κ轻链型FLC比率临界值，以更准确地识别进展为有症状浆细胞疾病风险增高的个体。
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