Combined use of free light chain and heavy/light chain ratios allow diagnosis and monitoring of patients with monoclonal gammopathies: Experience of a single institute, with three exemplar case reports

Abstract

Monoclonal gammopathies are characterized by serum monoclonal component (MC) plus an intact immunoglobulin and a free light chain (FLC), or a combination of both. The measurement of FLC with Freelite^® is the standard practice recommended by International Myeloma Working Group guidelines. Recently, Hevylite^® heavy/light chains (HLC) assays were introduced to specifically target junctional epitopes between the heavy and light chains of intact immunoglobulins, allowing the independent quantification of the involved (MC) and uninvolved (polyclonal immunoglobulin background) HLC isotype. Between January 2012 and March 2014, 90 patients were examined: 49 multiple myeloma (MM), 6 smoldering MM (SMM) and 35 monoclonal gammopathy of undetermined significance (MGUS). Of these 90 patients, 300 samples were collected at different times. The diagnostic and monitoring contribution of Hevylite A and G assays was assessed in all 90 patients examined. Additionally, 3 representative cases were selected. The Hevylite absolute values and ratio demonstrated high sensitivity and specificity with respect to serum protein electrophoresis and serum immunofixation. The combined use of Hevylite A and G with Freelite was particularly useful in dubious cases with more than one MC or with co-migrating components, as well as in the course of monitoring to assess the independent change of FLC and HLC, possibly reflecting the presence of clonal heterogeneity in the cohort. From this study, it can be concluded that FLC and HLC are independent, useful markers to monitor the MC and to assess with greater specificity and sensitivity the effect of therapy, thereby providing clinical support. Further studies are required to assess the prognostic potential of Hevylite in MGUS and SMM.

Keywords: free light chain; heavy/light chain; monoclonal gammopathy of undetermined significance; multiple myeloma; serum immunofixation; serum protein electrophoresis; smoldering myeloma.

Figure 1.

MGUS, MM and SMM patient frequency and MC type distribution in the study population. (A) Percentage of patients with MGUS, MM and SMM, accounting for 6, 26 and 68, of the population, respectively. (B) MC type frequency in the population, consisting of 42.8% IgGκ, 6.1% IgAλ, 32.6% IgGλ, 6.1% LCMM and 12.2% IgAκ MM patients. MM, multiple myeloma; SMM, smoldering MM; MGUS, monoclonal gammopathy of undetermined significance; Ig, immunoglobulin; MC, monoclonal component.

Figure 2.

Abnormality of FLCr in the overall population, and MGUS, SMM and MM frequency. FLC abnormality was present in 82% of all patients; among these samples, 69.9% were MM patients, 24.6% were MGUS patients and 5.5% were SMM patients. With regard to the remaining 18% of patients without FLCr abnormality, 37.5% were MM patients, 50% were MGUS patients and 12.5% were SMM patients. MM, multiple myeloma; SMM, smoldering MM; MGUS, monoclonal gammopathy of undetermined significance; FLC, free light chain; FLCr, FLC ratio.

Figure 3.

κ/λ FLCr abnormality in the three types of patients: MGUS, SMM and MM. κ/λ ratio abnormality in the three categories of MGUS, SMM and MM patients, accounted for 14.4, 41.0 and 63.6% of cases, respectively. MM, multiple myeloma; SMM, smoldering MM; MGUS, monoclonal gammopathy of undetermined significance; FLCr, free light chain ratio.

Figure 4.

Case 1: Hevylite^® G allowed quantification of the primary and secondary MC. (A) Hevylite G and Freelite^® absolute values and ratio, and (B) immunofixation in an IgGλ MM patient. As the intact immunoglobulin clone appeared to respond to therapy, with normalization of HLC G values, FLCs did not ever normalize, suggesting the presence of a secondary, independent clone of light chain-producing plasma cells, which prompted a change of treatment and autologous stem cell transplantation. Underlined values are outside the NR. HLC, heavy/light chains; FLC, free light chain; Ig, immunoglobulin; MC, monoclonal component; dFLC, difference between FLCκ and FLCλ; NR, normal range; Spc, serum protein components; tot, total.

Figure 5.

Case 2: HLC and FLC persistent abnormality predicts relapse prior to the clinical symptoms. (A) Hevylite^® G and Freelite^® absolute values and ratio, and (B) sPEP profile in an IgAλ and FLCλ MM patient. The high FLCλ (48 mg/l) and FLCr (0.14) levels in November 2012 indicated the presence of residual disease for this patient who previously underwent 5 cycles of therapy with melphalan and prednisone. From June 2013, the sPEP profile showed an MC in the γ zone, which appeared increased in the subsequent monitoring. This was accompanied by the observation of FLC and HLC absolute and ratio abnormal values. Underlined values are outside the NR. HLC, heavy/light chains; FLC, free light chain; Ig, immunoglobulin; MC, monoclonal component; dFLC, difference between FLCκ and FLCλ; NR, normal range; HLCr, HLC ratio; sPEP, serum protein electrophoresis; NI, not identified.

Figure 6.

Case 3: HLC and FLC persistent abnormality predicts relapse prior to the clinical symptoms. (A) Hevylite^® G and Freelite^® absolute values and ratio, and (B) sPEP profile in an IgAκ MM patient. This patient exhibited a monoclonal IgAκ in the β2 zone of the sPEP migration pattern. In September 2013, it was identified a secondary MC in the γ zone of the migration pattern, and Hevylite and Freelite assisted in clarifying the isotypes, allowing for subsequent monitoring. The IgGκ and IgGλ levels were below the NR; IgAκ was increased above the NR (9.08 g/l), whereas the IgAλ was suppressed (0.017 g/l), with a highly abnormal HLC A ratio. In November 2013, there was an improvement in the biochemical parameters of IgGκ and IgGλ, the HLC ratio became closer to the NR, and there was a reduction in dFLC and HLC A. In February 2014, the secondary IgG MC was no longer visible, whereas the IgA HLC and FLC were increased and highly above the NR. HLC A and FLC steadily increased over the next months, until the patient succumbed in October 2014. Underlined values are outside the NR. HLC, heavy/light chains; FLC, free light chain; Ig, immunoglobulin; MC, monoclonal component; dFLC, difference between FLCκ and FLCλ; NR, normal range; HLCr, HLC ratio; sPEP, serum protein electrophoresis.