Patient characteristics at baseline are shown in . Patients were followed up for a median of 46.1 months (range: 0.5–157.8). Previous assessment of HLC concentrations in normal blood donors established median HLC ratios and 95% ranges of 1.74 (1.12–3.21) for IgGκ/IgGλ17
and of 1.18 (0.78–1.94) for IgAκ/IgAλ.18
Results of HLC testing revealed 5% of control sera lying outside but very close to the verge of the normal range, and an abnormal HLC ratio in all patients of this study (, respectively) including 18 patients with oligosecretory disease (<10
g/l, 7 IgG and 11 IgA).
Figure 1 Scatter graph of the HLC values. All individual values of the 100 patients with IgG (a) and of the 56 patients with IgA M-Ig (b) were outside the normal range. The solid squares denote patients with quantifiable M-Igs by SPEP, whereas open squares denote (more ...)
Accurate measurement of M-Ig by SPEP densitometry was not possible in 46% (26/56) IgA and 4% (4/100) IgG patients because the M-Ig had been obscured by other proteins, mostly because of migration toward the β region. Quantitative HLC measurements were possible in all patients, even in those with M-Ig difficult to be quantified by SPEP. Summated Ig′κ+Ig′λ correlated well to total Ig for each isotype measures; IgG (r2=0.93), IgA (r2=0.94).
Myeloma responses were assessed after induction therapy by conventional techniques. CR and nCR were noted in 31 (20.8%) and 17 (11.4%) of all patients; 18 (12.1%) were categorized as VGPR, 46 (30.9%) as PR and 18 (12.1%) as minor response, respectively, yielding an overall response rate (CR–PR) of 75.2%. Eight (5.4%) patients presented with stable disease and 11 (8%) with progressive disease. At time of best response, exact quantification by SPEP was not possible in two patients with minor response, seven patients with PR, and one patient with VGPR. HLC ratios could be determined in all of those patients and were abnormal in all. The distribution HLC ratios at baseline was similar in patients with subsequent different response categories (P=0.451), thus baseline HLC levels did not predict the quality of response after induction therapy (). Measurement of HLC ratio at best response yielded significantly different results in the various response groups (P<0.006).
Figure 2 Box and whisker representation of HLC ratios of the involved monoclonal immunoglobulin at baseline and maximal response for patients classified according to the IMWG and EBMT (minor response) criteria. HLC ratio at baseline did not differ between patients (more ...)
shows the results of HLC, FLC, IFE and SPEP testing in patients at time of best response. Of note, an abnormal HLC ratio was seen in 8 of the 31 patients in CR; four of them had abnormal HLC ratio only, whereas in the other four both an abnormal HLC and FLC ratio were noted. In the 17 patients with nCR and the 18 patients with VGPR, an abnormal HLC ratio was observed in 9 and 14 patients, respectively, with 8 and 10 each having both abnormal HLC and FLC ratio.
Results of HLC, FLC, IFE and SPEP testing in patients with different response categories
show a typical follow-up of individual patients with sequential testing and the additional use of HLC ratios. Patient A achieved a CR established by SPEP and IFE, but an abnormal HLC ratio indicated the presence of M-Ig at a time when an M-Ig was no longer detectable by IFE (). With further follow-up and continued CR, the HLC ratio became normal. In this patient, the kinetics of FLC ratio corresponded with the changes of the HLC ratio during the entire follow-up. Patient B already achieved CR after induction therapy. At the time of first documentation of CR, which occurred before the start of high-dose melphalan, both HLC ratio and FLC ratio also became normal (). The patient remained in IFE-negative CR for 14 months, but the HLC ratio became abnormal 7 months after the first achievement of a normal HLC ratio, indicating an evolving relapse. At that time, total IgA and IgAκ were still within the normal range. During subsequent testing, IFE became positive 5.5 months after the HLC ratio had changed from normal to abnormal. Later, SPEP became positive, with further increase in the HLC ratio. With marked delay, clinical relapse also became apparent. These patterns indicated the presence of M-Ig, while IFE already had become negative or pointing to imminent relapse while IFE was still negative, have been observed in three patients each.
Figure 3 Sequential SPEP, IFE, HLC ratios, and FLC ratios in two patients with IgAκ myeloma. In patient A (a), IFE became negative at a time when abnormal HLC ratio and FLC ratio still indicated presence of residual disease. Both later tests became normal (more ...)
Median survival of the entire patient cohort was 53.5 months. When patients were stratified according to either abnormal (0.022–45) or highly abnormal (<0.022 or >45) presentation HLC ratio values, survival was significantly shorter in those with highly abnormal ratios (median 40.5 months vs median not reached, hazards ratio (HR): 2.07, confidence interval (CI): 1.15–3.75, P=0.016) (). The survival rates at 5 years were 33.4% for the former and 58.9% for the latter group (P=0.01). For patients with a highly abnormal FLC ratio (<0.1 or >30), a statistically not significant tendency for shorter survival was noted (40.8 months vs median not reached, HR: 1.72, CI: 0.93–3.17, P=0.08) compared with those with less abnormal FLC ratios (0.1–30).
Figure 4 Overall survival in patients stratified by HLC ratio. Median survival was 40.5 months in patients with highly abnormal HLC ratio (red line) and was not reached in those with less abnormal HLC ratio (blue line, P=0.016) (a). Patients achieving a PR or (more ...)
When survival was analyzed from time of first achievement of maximal response (PR or better), patients with HLC ratios remaining abnormal had a significantly shortened survival as compared with those achieving a normal HLC ratio (40.5 months; CI: 17–65 vs median not reached, HR: 2.8, CI: 0.99–8.3, P<0.03) (). A similar, but statistically not significant tendency was noted in the patients who achieved VGPR or better (median not reached, HR: 2.1, CI: 0.6–7.5, P=0.2) ().
Univariate Cox analysis associated an increasingly abnormal HLC ratio (<0.022, >45) and a β2-microglobulin concentration of >5.5mg/l at presentation with shorter survival (HR 1.88, CI: 1.1–3.1, P=0.015 and HR 2.2, CI: 1.3–3.9, P=0.016, respectively), whereas for the other parameters tested (FLC ratio, albumin >35g/l, lactate dehydrogenase >248 U/l) no correlation was found (). Results of multivariate Cox analysis proved a highly abnormal HLC ratio and highly abnormal β2-microglobulin as parameters independently associated with survival (HR: 1.94, CI: 1.1–3.3, P=0.016, and HR: 2.01, CI: 1.1–3.6, P=0.016, respectively).
Univariate and Cox regression multivariate analysis of prognostic parameters with survival