The serum immunoglobulin free light chain (FLC) assay quantitates free kappa (κ) and lambda (λ) light chains. FLC elevations in patients with diffuse large B-cell lymphoma (DLBCL), Hodgkin lymphoma (HL), and chronic lymphocytic leukemia (CLL) are associated with an inferior survival. These increases in FLC can be monoclonal (as in myeloma) or polyclonal. The goal was to estimate the frequency of these elevations within distinct types of B-cell and T-cell non-Hodgkin lymphoma (NHL) and whether the FLC measurements are associated with event-free survival (EFS). We studied serum for FLC abnormalities using normal laboratory reference ranges to define an elevated κ or λ FLC. Elevations were further classified as polyclonal or monoclonal. Four hundred ninety-two patients were studied: 453 B-cell and 34 T-cell NHL patients. Twenty-nine % (142/453) of patients had an elevated FLC of which 10% were monoclonal elevations. Within B-cell NHL, FLC abnormalities were most common in lymphoplasmacytic (79%), mantle cell (68%), and lymphomas of mucosa associated lymphoid tissue (31%); they were least common in follicular (15%). The hazard ratio (HR) for EFS in all patients was 1.41 (95% CI; 1.11-1.81); in all B-cell NHL the HR was 1.44 (95% CI 1.11-1.96); in all T-cell NHL the HR was 1.17 (95% CI 0.55-2.49). FLC abnormalities predicted an inferior OS (HR=2.75, 95% CI: 1.93-3.90, P<0.0001). The serum FLC assay is useful for prognosis in both B-cell and T-cell types of NHL. In B-cell NHL further discrimination between a monoclonal and polyclonal elevation may be helpful and should be analyzed in prospective clinical trials.
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