Clinical and Cytogenetic Characterization of Light Chain Amyloidosis Patients with a Low Amyloidogenic Free Light Chain Count at First Diagnosis

Background: Systemic light chain amyloidosis (AL) is a rare and life-threatening protein-deposition disorder. The diagnosis and especially quantification of the underlying, usually small clonal B cell disorder in patients with very low levels of free kappa or lambda light chains in serum (FLC) can be challenging. DFLC (difference of involved minus uninvolved FLC) response to therapy is hardly assessable for initial values below 50 mg/l. Consequently, these patients are frequently excluded from prospective and retrospective studies.

Objective: Characterization of AL amyloidosis patients with dFLC<50.

Methods: We have retrospectively analysedthe clinical features and long-termoutcome of 611 newly diagnosed AL patients with available dFLC and cytogenetic evaluation by iFISH at their first visit to our center between 2003-2014.

Results: Clinical characteristics and detailed results are depicted in table 1. Patients with dFLC<50 significantly showed lower bone marrow plasma cell counts (6% vs. 10%, p<0.001), M-spike (7 g/l vs. 9 g/l, p<0.001) and concentrations of the monoclonal heavy chain (7 g/l vs. 10 g/l, p=0.003), while the mere presence of a monoclonal heavy chain in immunofixation (IF) was more frequent in these patients (55% vs. 38%, p=0.003). All analysed chromosomal aberrations were not associated with dFLC<50 (all p-values >0.05). Patients with cardiac (40% vs. 82%, p<0.001) and soft tissue (26% vs. 42%, p=0.005) involvement, higher Mayo Score and lower Karnofsky Index (KI) were much less frequently found in the group with initial dFLC<50, while kidney involvement was more common (85% vs. 58%, p<0.001). This, however, was not associated with a significantly worse renal function at diagnosis. Median overall survival (OS) was significantly better in patients with dFLC<50 regardless of treatment type (Figure 1): Bortezomib (77 vs. 16 months, p=0.006), Melphalan-Dexamethason (Mdex, 96 vs. 19 months, p=0.001) and high-dose Melphalan (HDM, not reached vs. 99 months, p=0.005).

Conclusion: AL patients with an initial dFLC<50 mg/l represent a distinct clinical entity characterized by infiltration of the marrow with a small plasma cell clone and frequent presence of a monoclonal intact heavy chain, but with a low clonal heavy chain load. Importantly, this group of patients is not associated with any particular chromosomal aberrations as revealed by iFISH. This entity is further associated with a distinct pattern of organ involvement, i.e. a low Mayo Score, more than 80% of patients with renal amyloidosis, and very favourable OS irrespective of primary treatment regimens. Results of prospective clinical trials might be adversely influenced by the exclusion of these patients.

Figure 1.

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Figure 1.

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