Serum Free Light Chain Predict Overall Survival and Response to Therapy in Patients with Newly Diagnosed Multiple Myeloma

Background: Multiple myeloma is characterized by underlying clinical and biological heterogeneity, which translates to variable responses to treatment and outcome. Methods: To assess the roles of serum free light chain (sFLC) and K/L FLC ratio (rFLC) in the diagnoses and prognoses of multiple myeloma (MM), sFLC levels and K/L ratios were measured in 112 patients with newly diagnosed multiple myeloma using the Freelite automated immunoassay. Results: Abnormal sFLC and/or rFLC levels were detected 99.1% of the patients. The baseline sFLC predicted the overall survival (OS). The median OSs were not reached (NR) and were 30 months in the low sFLC group (sFLC-K < 132 mg/L or sFLC-L < 342 mg/L) and the high sFLC group (sFLC-K >= 132 mg/L or sFLC-L >= 342 mg/ L) (p < 0.001), respectively. Similarly, the rFLC successfully predicted the OS times of 29 months for group A (rFLC <= 0.03 or >= 32) and NR for group B (0.03 < rFLC < 32) (p < 0.001). According to the response to treatment and sFLC ratio, significant differences in the OSs were observed between the partial response group and other patients, (respectively, OS median = 28 months vs. NR, log rank p < 0.001). Additionally, the patients were further stratified into two groups using the novel poor-prognosis factors (rFLC > 32 or < 0.03) combined with the International Staging System parameters (beta2-microglobulin, albumin), i.e., a low-risk group (those with zero or one factor) and a high-risk group (those with two or three factors). The median OSs for the low- and high-risk groups were NR and 29 months, respectively (p = 0.001). Conclusions: The sFLC assay was extremely sensitive in the diagnosis of MM. In addition to its strong prognosis value, it could be a predictor of response to therapy.