Clinical presentation and prognosis of light-chain amyloidosis patients with unmeasurable free light-chain levels.

To summarize distinct clinical characteristics and prognoses associated with and validate the novel hematologic response criteria in Chinese light-chain amyloidosis patients with a difference between involved and uninvolved free light chain (dFLC) < 50 mg/L. We retrospectively compared clinical features and outcomes between patients in the dFLC < 50 mg/L group (n = 74) and the ≥ 50 mg/L group (n = 248). Patients with dFLC < 50 mg/L presented less frequent and less severe cardiac involvement, but higher renal involvement. Additionally, more patients in the dFLC < 50 mg/L group showed intact immunoglobulin monoclonal protein and high immunoglobulin monoclonal protein levels. Moreover, patients in the dFLC < 50 mg/L group had significantly superior progression-free survival (PFS; not reached vs. 16.0 months; p < 0.001) and overall survival (OS; not reached vs. 41.0 months; p < 0.001) as compared with those in the dFLC ≥ 50 mg/L group. Furthermore, we confirmed that achieving complete response (CR) or low dFLC partial response (PR) predicted better OS in patients with initial dFLC ≥ 20 mg/L (not reached vs. 19 months; p = 0.005). Patients with initial dFLC < 50 mg/L represented distinct clinical manifestations and outcomes. Achieving CR or low dFLC PR might represent potential therapy goals allowing better survival and organ response in patients with dFLC between 20 and 50 mg/L.