Prognostic value of involved/uninvolved free light chain ratio determined by Freelite and N Latex FLC assays for identification of high-risk smoldering myeloma patients

Basile Henriot (1) , Emmanuel Rouger (1) , Chloé Rousseau (1) , Martine Escoffre (1) , Martine Sébillot (1) , Claude Bendavid (2, 1) , Stephane Minvielle (3) , Hervé Avet-Loiseau (4) , Olivier Decaux (1) , Caroline Moreau (2, 1)

1 Centre Hospitalier Universitaire de Rennes [CHU Rennes] = Rennes University Hospital [Ponchaillou]
2 NuMeCan - Nutrition, Métabolismes et Cancer
3 CRCINA-ÉQUIPE 11 - Integrative Oncogenomics of Multiple Myeloma Pathogenesis and Progression
4 IUCT Oncopole - UMR 1037 - Institut Universitaire du Cancer de Toulouse - Oncopole

Background Smoldering multiple myeloma (SMM) is an asymptomatic plasma cell disorder with a high risk of progression to symptomatic multiple myeloma (MM). The serum free light chain (sFLC) ratio is a powerful prognostic factor for SMM an sFLC ratio ≥8 has been reported to be associated with a high risk of progression to MM, and an sFLC ratio ≥100 has been described as a criterion for ultra-high-risk SMM, and has been integrated into the definition criteria for MM since 2014. However, all recommendations were based on sFLC measured using the first commercialized assay, Freelite™, while other assays are now available. We aimed to evaluate the safety and accuracy of N-Latex sFLC to identify high-risk and ultra-high-risk SMM.Methods The sFLC ratio was measured at diagnosis with both Freelite and N-Latex assays in a cohort of 176 SMM patients on a BN Prospec nephelometer. Demographic, clinical, therapeutic and laboratory data were collected at the time of diagnosis and at follow-up.Results Sixty-two patients (35.2%) progressed to MM within 2 years. Compared to Freelite™ sFLC, N Latex sFLC ratios ≥8 and ≥100 provided similar performances for the identification of high-risk and ultra-high risk SMM patients.Conclusions Our results evidenced that the N-Latex assay could be used for SMM monitoring, like Freelite. However, an N-Latex sFLC ratio ≥70 appears to provide similar performances to a Freelite sFLC ratio ≥100, with a slightly better positive predictive value. Both assays provided accurate identification of high-risk and ultra-high risk SMM patients. These results should be confirmed in an independent study.

Mots clés: myeloma; free light chains; smoldering multiple myeloma; high-risk

Domaines: Cancer; Hématologie

Basile Henriot, Emmanuel Rouger, Chloé Rousseau, Martine Escoffre, Martine Sébillot, et al.. Prognostic value of involved/uninvolved free light chain ratio determined by Freelite and N Latex FLC assays for identification of high-risk smoldering myeloma patients. Clinical Chemistry and Laboratory Medicine, 2019, 57 (9), pp.1397-1405. ⟨10.1515/cclm-2018-1369⟩. ⟨hal-02120882⟩