Application of cerebrospinal fluid free light chain in diagnosis of primary central nervous system lymphoma and monitoring of associated chemotherapy efficacy

Cerebrospinal fluid (CSF) free light chain (FLC) detection has been proposed as a tool for diagnosing primary central nervous system lymphoma (PCNSL), but there is no consensus on the appropriate reference range and its value for monitoring chemotherapy efficacy has not been investigated in Chinese PCNSL patients. We assessed the application potential of CSF FLC ratios for diagnosing PCNSL and monitoring associated treatment efficacy. Kappa (κ) and lambda (λ) FLC were measured by nephelometry in CSF samples of patients with PCNSL (n = 45), other neurological diseases (n = 30), and normal controls (n = 60). Results of κ/λ FLC ratios (FLCr) were correlated with patients’ diagnoses and receiver operating characteristic analysis was used to determine accuracy. In PCNSL patients, FLCr analysis was compared between PCNSL before and after treatment. κ FLC and FLCr concentrations in PCNSL were significantly higher than in patients without PCNSL (P < 0.05). The optimal cut-off for FLCr was 0.35, with diagnostic sensitivity and specificity of 78% and 72%, respectively. FLCr concentrations decreased after chemotherapy. CSF FLC is a novel biomarker for diagnosis and chemotherapy efficacy monitoring in PCNSL.