Hevylite and Freelite Tests in Newly Diagnosed Multiple Myeloma: Clinical Utility and Correlations with Clinical Features

Introduction Heavy light chain (HLC) assay is a recently developed method that separately quantifies the k and L-bounded amounts of a given intact immunoglobulin (Ig). It allows an accurate quantification of both the involved/uninvolved Ig and permits to quantify even small monoclonal protein. Free light chain (FLC) and HLC can provide prognostic information for multiple myeloma patients.

We evaluated the role of HLC and FLC tests in the assessment and evolution of the disease in newly diagnosed multiple myeloma (MM) patients.

Methods From February 2011 to April 2014, 1510 patients aged ≤65 years with symptomatic newly diagnosed MM were enrolled in the EMN02/HO95 study. Details about treatments and preliminary results of the main study were previously reported (Cavo M et al, abs8000, J Clin Oncol 34, 2016). In this analysis, we focused on patients enrolled in Italy (N=718). Serum samples from each enrolled patient were collected at diagnosis, before starting maintenance, and thereafter every 6 months. Samples from 665 patients at diagnosis and 156 at pre-maintenance were analyzed.

Involved HLC ratio (iHLCR) was calculated with the involved Ig (either G or A) as numerator. Involved FLC ratio (iFLCR) was calculated as K/L or L/K with the monoclonal chain as numerator. FLC ratio (FLCR) and HLC ratio (HLCR) were calculated as K/L. The analyses were performed using Spearman correlation.

Results Median follow-up was 32 months. At baseline the type of paraprotein was IgG in 428 (298 IgG-k, 130 IgG-L), IgΑ in 123 (77 IgΑ-k, 46 IgΑ-L) or light chain in 104 patients (k 73, L 31); 10 patients were IgD or IgM. International Staging System (ISS) stages were well distributed in all the isotypes.

The median involved HLC values were IgG-K 28.97, IgG-L 30.6, IgA-K 41.7, IgA-L 35.7 g/L, light chain K 2719.58 mg/L, and light chain L 3369.75 mg/L.

HLC IgG was significantly correlated with B2-microglobulin (r=0.31), extensive bone marrow infiltration >60% (r=0.31) and hemoglobin (r=-0.39). HLC IgA was not correlated with any disease parameter.

In light chain MM, iFLC was correlated to B2-microglobulin (r=0.41), creatinine (r=0.39), extensive bone marrow infiltration >60% (r=0.39) and hemoglobin (r=-0.36).

The increase of iFLCR (≥ median value) was significantly associated with IgG, ISS III, anemia, extensive bone marrow infiltration and higher creatinine (p<0.001), but not with the presence of high risk chromosomal abnormalities. High iFLCR (> third quartile) was significantly associated with inferior TTP (median 43.4 versus NR, HR 1.75 95% CI 1.22-2.53, p 0.003).

The increase of iHLCR (≥ median value) was significantly associated with ISS III, anemia, and extensive bone marrow infiltration (p<0.001), whereas the presence of high risk chromosomal abnormalities was not.

At pre-maintenance, 17% of patients had an abnormal HLCR, whereas 82% had a normalization of HLCR. The normalization of HLCR before starting maintenance was significantly related with the achievement of complete response (CR) (p=0.02) and a trend towards a longer 3-years TTP was observed (83% versus 74%, Log-rank test 0.05).

Before start of maintenance, 27% of patients had a normalization of FLCR. No significant correlation with response or outcome was observed for patients who had a normalization of FLCR.

At pre-maintenance, 67% IgG or IgA MM patients were immunofixation (IFX) negative. Among them, 8% had still an abnormal HLCR compared to IFX positive patients (8% versus 36%, p<0.001).

Conclusions This preliminary analysis confirms the prognostic role of high iFLCR and iHLCR in newly diagnosed MM patients. HLCR normalization may be a valuable parameter to better define CR and predict outcome. HLC can quantify even small monoclonal protein when immunofixation is negative. Further follow-up is needed to assess the prognostic impact of HLC and FLC on survival outcome. Updated results will be presented at the meeting.