Intact immunoglobulin MM (IIMM) - sFLCs at diagnosis

From Wikilite

11.1. Introduction

Figure 11.1 The same microscope field of an IgGκ bone marrow sample showing dual populations stained with anti-IgG FITC and anti-κ TRITC. In addition, anti-BrDU staining of nuclei has been performed to show cells in S-phase of the cell cycle. Upper panel shows anti-IgG FITC cytoplasmic and anti-BrDU FITC nuclear staining, middle shows the same field with anti-κ TRITC staining and lower shows a double exposure of the 2 upper plates superimposed to demonstrate double stained IgGκ cells (yellow), κ only cells (red) and S-phase cells with green nuclei. Arrows indicate BrDU+ and BrDU- M-Ig+ cells, BrDU+ and BrDU-k only cells together with non-plasma cells in S-phase. (Reproduced with permission from Haematologica and M Ayliffe ^[1]).

Figure 11.2 Classification of 95 cases according to the presence of FLCs in the urine (Bence Jones protein +ve or negative) and cell populations demonstrated in the marrow (IIM-Ig and/or FLC only) together with their incidence, immunochemical findings and survival since diagnosis. (Reproduced with permission from Haematologica and M Ayliffe^[1]).

Approximately 80% of patients with MM produce intact immunoglobulin monoclonal proteins (Figure 7.3) of whom ~50% have excess monoclonal FLCs in urine by IFE ^[2]. SPE and serum IFE tests for FLCs are less frequently positive because of low sFLC concentrations.

The first attempt to measure serum FLC in IIMM was by Sölling ^[3] in 1982. Using column chromatography, FLCs were separated from bound light chains prior to their measurement by antibodies against whole light chains. He showed that monoclonal sFLCs were present in 86% of IIMM patients. Recently, using sensitive serum FLC immunoassays, many authors have shown even higher prevalence of monoclonal FLCs. These studies, together with their clinical relevance are described in this chapter.

11.2. Myeloma cell diversity: production of monoclonal immunoglobulins and FLCs

Myeloma plasma cells have huge genetic and mophological diversity so mixed clones occur at clinical presentation. Subsequent evolutionary selection by chemotherapy leads to escape mutants with different protein expression profiles. Predictably, myeloma cell populations with mixed monoclonal protein expression arise from this diversity. Perhaps surprisingly, this was only recently confirmed by histology. Using a double immunofluorescence staining method, Ayliffe et al. ^[1], produced an estimate of different types of plasma cells in bone marrow biopsies (Figure 11.1). In many patients, single populations of cells were present: 74% contained only intact monoclonal immunoglobulins and 8% only monoclonal FLCs. However, 18% contained a mixture of both cell populations (Figure 11.2). They also showed that progression from cells making intact monoclonal immunoglobulins to cells restricted to FLC production alone occurred in some patients during the course of their disease. Furthermore, the presence of “FLC-only” cells was associated with shortened survival. This indicates that monoclonal FLC production at a cellular level is an adverse prognostic marker both at clinical presentation and during relapse of patients with IIMM. The relationship between monoclonal FLC production and poor survival has been observed in a series of studies that are described below.

11.3. Serum FLC concentrations at disease presentation

Figure 11.3 Concentrations of FLCs in 314 patients with IgG MM compared with 282 normal sera.

Figure 11.4 Concentrations of sFLCs in 142 IgA, 36 IgD and 5 IgE MM patients compared with 282 normal sera.

Figure 11.5 Frequency of abnormal sFLC concentrations in patients with different types of MM and Waldenström's macroglobulinaemia (WM).

Figure 11.6 sFLCs in 55 IgG and 14 IgA MM patients who had no urine FLC excretion compared with 282 normal sera.

Figure 11.7 Serum monoclonal IgGκ measured by scanning densitometry, and sFLC κ concentrations in 150 IgG kappa MM patients. (Pearson rank correlation r = -0.015).

Figure 11.8 Serum monoclonal IgGλ measured by scanning densitometry, and sFLCλ concentrations in 116 IgGλ MM patients. (Pearson rank correlation r = -0.0037).

Figure 11.9 Relationship between SWOG disease stage (South West Oncology Group) and the presence of proteinuria or abnormal serum FLC κ/λ ratios in 289 patients (364 serum samples) studied in a MM clinic. (Courtesy of MR Nowrousian).

Figure 11.10 A. Disease-specific survival of MM patients according to baseline sFLC κ/λ ratios.* B. Disease-specific survival of MM patients according to abnormalities of baseline sFLC κ/λ ratios, serum albumin or β₂-microglobulin as used in the International Staging System. (Courtesy of M-C Kyrtsonis).

Figure 11.11 Kaplan-Meier overall survival plot according to tertiles of baseline concentrations of sFLCs. Outcome was inferior among patients with top-tertile sFLC baseline levels. (This research was originally published in Blood ^[4] © the American Society of Hematology).

Figure 11.12 Kaplan-Meier overall survival plot according to tertiles of baseline concentrations of sFLCs.Outcome was superior among patients with bottom-tertile sFLC baseline levels. (This research was originally published in Blood ^[5] © the American Society of Hematology).

Mead et al.^[6], assessed sFLC concentrations, at the time of presentation, in 314 patients with IgG, 142 with IgA and 36 with IgD MM using archived samples from the UK, MRC MM trials. Overall, 88% had elevated sFLCs with the following breakdown: IgG 84%, IgA 92% and IgD 94%, and in all of 5 IgE patients. Some of the remaining patients had normal or reduced concentrations of FLCs but their κ/λ ratios were abnormal, indicating monoclonality in association with bone marrow suppression. In total, 96% of all MM patients (including LCMM and NSMM) had abnormal FLC concentrations or abnormal κ/λ ratios (Figures 11.3 to 11.6). This percentage is higher than previously reported ^[2][3] , reflecting the increased sensitivity of the FLC immunoassays and, in particular, the use of the suppressed alternate FLC to identify abnormal κ/λ ratios. It is also of note that there was complete concordance between the monoclonal FLC type identified by κ/λ ratios and IFE (Figure 11.3). This provided an important specificity validation of the FLC immunoassays.

Other large studies of MM at disease presentation have shown similar results. Orlowski et al. ^[7], studied sFLCs in 487 patients and noted that 94% had abnormal sFLC κ/λ ratios. Snozek et al. ^[8], reported that monoclonal sFLCs were present in 95% of 576 MM patients at disease presentation, an identical figure to that of Owen et al. ^[9], in 207 patients entered into the UK, MRC trials. Finally, Dispenzieri et al. ^[5], observed abnormal sFLC κ/λ ratios in 96% of 399 patients.

As sFLC concentrations are normal in some patients with IIMM, it is clear that serum electrophoretic tests are essential for myeloma diagnosis. In contrast, sFLC assays are more sensitive for the identification of FLCs in LCMM and NSMM. Therefore, when MM is suspected, the optimum laboratory practice should be to test sera by both SPE/IFE and sFLC assays.

In the study by Mead et al. ^[6], sFLC concentrations were higher in IgA than IgG patients but highest in IgD patients (similar to LCMM patients (see Figure 11.4). High levels of uFLC excretion and excess of λ compared with κ are typical of IgDMM ^[10][11] . Five patients with IgE multiple myeloma are included in Figure 11.4. Although the number of patients is small, the FLC results are presumably representative of the disease.

A subgroup of 69 patients with IIMM (55 IgG and 14 IgA), who had no detectable uFLC excretion (less than 40mg/L), is shown in Figure 11.6. Serum analysis showed that 95% of the patients had abnormal FLC κ/λ ratios. It is of note that none of the patients had increased concentrations of the alternate sFLC, indicating there was insignificant renal impairment. At clinical presentation there was no correlation between serum creatinine and sFLC levels (as for LCMM - Figure 8.3).

It was also apparent that sFLC measurements showed no significant correlation with serum levels of intact monoclonal immunoglobulins (by Pearson correlation coefficient r). Results for IgGκ and IgGλ are also shown in Figures 11.7 and 11.8.

This lack of correlation is an important issue because it indicates that serum FLC concentrations are independent markers of the disease process in IIMM. sFLCs provide additional disease information, both at initial presentation and when monitoring patients.

11.4. Disease stage and sFLCs

It has been known for some time that in MM, high monoclonal urine FLC excretion at clinical presentation is predictive of poor survival, and hence, disease stage. For example, the outcome for 351 patients with LCMM was compared with 1,512 IgG and 717 IgA patients entered into the UK, MRC myeloma multicentre trials ^[12]. LCMM patients had the shortest median survival of 1.9 years (P<0.001) compared with 2.3 years for IgA patients and 2.5 years for IgG patients. It follows that sFLC measurements should be of more value than urine FLCs because of greater clinical sensitivity and analytical accuracy.

One early study noted the relationship between FLC proteinuria, abnormal sFLC κ/λ ratios and SWOG MM staging system (South West Oncology Group) in a cohort of 289 patients (MR Nowrousian - personal communication). Patients with advanced disease were more likely to have Bence Jones proteinuria or abnormal sFLC concentrations (Figure 11.9).

Several recent studies have assessed the relationship between sFLCs at disease presentation and subsequent outcome. Kyrtsonis et al. ^[13], investigated the prognostic value of baseline sFLC κ/λ ratios in 94 MM patients. The median baseline ratio for κ MM (κ/λ ratio) was 3.57 and for λ MM (λ/κ ratio) was 45.1. sFLC ratios above the observed median values correlated with elevated serum creatinine and lactate dehydrogenase, extensive marrow infiltration and κ or λ light chain type of the intact monoclonal immunoglobulins. Importantly, the 5-year disease specific survival was 82% in patients with sFLC κ/λ ratios lower than the median compared with 30% for κ/λ ratios equal to or greater than the median (P<0.001) (Figure 11.10A).

In current myeloma practice, patients are categorised using the International Staging System (ISS) based upon serum albumin and β₂-microglobulin measurements alone. Kyrtsonis et al. ^[13], assessed these parameters alongside sFLC and showed that κ/λ ratios were an additional independent prognostic factor. Combination of the ISS with sFLC ratios in newly diagnosed MM patients for time to progression and survival (Table 11.1), showed significantly worse survival with abnormal sFLC ratios (P<0.0001)(Figure 11.10B).

In a similar study of 576 patients at the Mayo Clinic, abnormal sFLC ratios at presentation were again important independent markers of outcome. Snozek et al. ^[8], showed that sFLC ratios assessed alongside the ISS in patients with 0, 1, 2 or 3 risk factors (sFLC κ/λ ratios <0.03 or >32, β₂-microglobulin >3.5g/L and albumin >35g/L) had median overall survival times of 51, 39, 30 and 22 months respectively (P<0.001). Because these data provided additional information about outcome it was suggested that sFLC ratios should be incorporated into the ISS to provide a new risk stratification model.

van Rhee et al. ^[4], studied the relationship between sFLCs and outcome in 301 patients undergoing intensive treatment (Figure 11.11). They observed that baseline top-tertile sFLC levels >750 mg/L were associated with inferior overall (p=0.005) and event-free survival (p=0.007). Baseline concentrations of other serum or urine immunoglobulins (excluding β₂-microglobulin and albumin) did not identify prognostic subgroups. In an associated investigation, Cavallo et al. ^[14], indicated that sFLC concentrations and abnormal κ/λ ratios were both highly correlated with cytogenetic abnormalities and MM staging.

While results from these different studies show that both sFLC concentrations and sFLC ratios are prognostic, it is unclear which is preferable. Should it be sFLC κ/λ ratios, absolute values or subtracted FLC concentrations (involved minus uninvolved)? This question was recently addressed by Dispenzieri et al. ^[5], when analysing the outcome of 399 MM patients at clinical presentation. Patients were divided into terciles, and regardless of the baseline variable used (i.e. FLC ratios, involved FLCs or subtracted FLCs), patients with the lowest tercile of FLC had the best outcomes when compared with the two higher terciles. The outcomes for the two higher terciles were nearly identical (Figure 11.12). The respective median overall survivals were 49.4, 41.7 and 42.1 months, and the median progression free survivals were 34.9, 28.7 and 29.5 months.

Since high sFLCs frequently cause renal damage because of their inherant toxicity, the reduced survival might be related to renal associated mortality. In a study of sFLC concentrations in patients presenting with renal failure, patients with the highest concentrations were more likely to have cast nephropathy and hence higher mortality (Chapter 13). However, such patients are not normally included in routine clinical trials so it is unclear what role renal impairment has in determining outcome in the above studies.

Table 11.1 Disease specific survival (DSS) in 207 newly diagnosed patients with MM according to the combined sFLC κ/λ ratios and and the International Staging System comprising serum albumin and β₂-microglobulin. (Courtesy of M-C Kyrtsonis).

References