Prognostic value of serum immunoglobulin free light chains in multiple myeloma in real clinical practice

The diagnostic and prognostic value of the study of serum immunoglobulin free light chains kappa and lambda (FLC-κ and FLC-λ) and their ratio (FLC κ/λ) in patients with multiple myeloma (MM) was evaluated. The study involved 206 patients with newly diagnosed MM which were observed in Novosibirsk Hematology Center from 2012 to 2017. The median age of the subjects was 67 years (32–82 years). The control group included 56 conditionally healthy individuals: 34 women (60.7%), 22 (39.3%) men, and the median age in this group was 62 years (40–68 years). The concentration of FLC-κ and FLC-λ (mg/l) in blood serum was determined by immunoturbidimetric method.

It was found that in patients with MM, the secretion level of serum FLC-κ or FLC-λ was statistically significantly higher in comparison with the control group and differed depending on the type of MM (p < 0.005). The diagnostic sensitivity of the quantitative determination of FLCs and their ratio in MM was 98.54%, compared with 94.17% in a standard immunochemical study. The values of the FLC κ / λ ratio < 0.04 or > 60, as well as the level of FLC-κ and FLC-λ are higher than the median obtained for the whole group (FLC-κ ≥ 702.0 and FLC-λ ≥ 493.2 mg/l); correlate with the known unfavorable prognosis factors for MM — with a high β2-microglobulin level (>3.5 mg/l) (r = 0.461, p < 0.001), plasma cell infiltration of bone marrow > 24% (r = 0.420, p < 0.001), and renal failure (creatinine > 173 μmol/l) (r = 0.380, p < 0.002), and also with a high level of LDH (>450 units/l) (r = 0.520, p < 0.001) — and are associate with an adverse outcome. The median overall survival (OS ) in the group of patients with FLC κ / λ < 0.04 or > 65 was 35 months compared with 60 months in the group with FLC κ / λ 0.04–65 (p < 0.001), 5-year OS — 42 and 75% respectively (p < 0.001).

Thus, the determination of serum FLCs in the blood serum of patients with MM increases diagnostic capabilities and can be used to assess the survival prognosis. The value of the FLC κ / λ ratio < 0.04 or > 65 allows us to divide patients with MM into risk groups with significantly different outcomes and can be used to identify patients with high risk who need more aggressive therapy and more detailed monitoring of the response to it.

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