Serum free light chains (sFLC) are independent prognostic markers of disease in light chain (AL) amyloidosis, and are used in the haematologic response criteria for treatment. However, up to 20% of patients have low sFLCs at diagnosis, with a difference between involved and uninvolved free light chains (dFLC) of less than 50 mg/L, making responses to treatment difficult to evaluate. In order to characterize this distinct subgroup of patients, we retrospectively analyzed 123 AL amyloidosis patients with dFLC <50 mg/L who were diagnosed between 2002 and 2013. The majority (n = 117) were treated for their AL amyloidosis, with over half (n = 68) receiving high-dose melphalan and autologous stem cell transplantation as first-line therapy. Overall they had a prolonged median survival of 9.2 years with less cardiac involvement (30%) and more renal involvement (76%). We also evaluated the newly proposed low dFLC partial response (PR) criteria, defined as a dFLC <10 mg/L if the initial dFLC 20-50 mg/L. The 14 patients with low dFLC PR had improved survival and organ responses compared with patients with no haematologic response. However, one-third of patients (n = 41) had an initial dFLC <20 mg/L so could not be evaluated. More sensitive methods of monitoring response to treatment for this subgroup population are still needed.
Keywords: AL amyloidosis; haematologic response; immunoglobulin light chain; stem cell transplantation; survival.