Purpose: To identify the criteria for hematologic and cardiac response to treatment in immunoglobulin light chain (AL) amyloidosis based on survival analysis of a large patient population. Patients and Methods: We gathered for analysis 816 patients with AL amyloidosis from seven referral centers in the European Union and the United States. A different cohort of 374 patients prospectively evaluated at the Pavia Amyloidosis Research and Treatment Center was used for validation. Data was available for all patients before and 3 and/or 6 months after initiation of first-line therapy. The prognostic relevance of different criteria for hematologic and cardiac response was assessed. Results: There was a strong correlation between the extent of reduction of amyloidogenic free light chains (FLCs) and improvement in survival. This allowed the identification of four levels of response: amyloid complete response (normal FLC ratio and negative serum and urine immunofixation), very good partial response (difference between involved and uninvolved FLCs [dFLC] < 40 mg/L), partial response (dFLC decrease > 50%), and no response. Cardiac involvement is the major determinant of survival, and changes in cardiac function after therapy can be reliably assessed using the cardiac biomarker N-terminal natriuretic peptide type B (NT-proBNP). Changes in FLC and NT-proBNP predicted survival as early as 3 months after treatment initiation. Conclusion: This study identifies and validates new criteria for response to first-line treatment in AL amyloidosis, based on their association with survival in large patient populations, and offers surrogate end points for clinical trials.

Key Points: A staging system based on proteinuria and glomerular filtration rate discriminates patients at different risk of progression to dialysis. Changes in proteinuria and glomerular filtration rate allow early assessment of renal response to therapy.

Key Points: Deep clonal responses improve outcomes and can change the natural history of advanced (cardiac stage III) AL amyloidosis. NT-proBNP >8500 ng/L and SBP <100 mm Hg identify a very poor risk subgroup of stage III AL amyloidosis.

Amyloidoses are characterized by organ deposition of misfolded proteins. This study evaluated immunohistochemistry as a diagnostic tool for the differentiation of amyloid subentities, which is warranted for accurate treatment. A total of 117 patients were systematically investigated by clinical examination, laboratory tests, genotyping, and immunohistochemistry on biopsy specimens. Immunohistochemistry enabled the classification in 94% of the cases. For subsequent analysis, the patient population was divided into 2 groups. The first group included all patients whose diagnosis could be verified by typical clinical signs or an inherited amyloidogenic mutation. In this group, immunohistochemical subtyping was successful in 49 of 51 cases and proved accurate in each of the 49 cases, corresponding to a sensitivity of 96% and a specificity of 100%. The second group included patients with systemic light chain amyloidosis without typical signs, senile transthyretin, or hereditary amyloidosis with a concomitant monoclonal gammopathy. Immunohistochemistry allowed to define the subentities in 61 of 66 (92%) of these cases. Immunohistochemistry performed by a highly specialized pathologist combined with clinical examination and genotyping leads to a high accuracy of amyloidosis classification and is the standard in our center. However, new techniques, such as mass spectroscopy-based proteomics, were recently developed to classify inconclusive cases.