CPD: Multiple Myeloma: Disease Overview and the Role of Genomics

AUTHORS:

Dr Roisin McAvera (Postdoctoral researcher)

Professor Siobhan Glavey (consultant haematologist & clinician scientist)

Introduction

Multiple Myeloma (MM) is a haematological malignancy characterised by clonal expansion of malignant plasma cells in the bone marrow. These plasma cells secrete a monoclonal immunoglobulin (Ig), often known as M-protein, which can lead to organ dysfunction, anaemia, renal impairment and bone fractures. MM affects around 400 people in Ireland each year, making it the second most common blood cancer. The median age of diagnosis is 66-70, however many patients are much younger at diagnosis making the disease less likely to be suspected. MM can arise from asymptomatic pre-malignant stages known as Monoclonal Gammopathy of Undetermined Significance (MGUS) and Smouldering MM (SMM) at a rate of 1% and 10% per year respectively. Although there are many new therapies available for MM, it remains incurable as eventually most patients will relapse or stop responding to treatment. As MM is a very heterogeneous disease, it can be challenging to detect initially and may not be suspected in patients under the age of 50. Prognosis varies widely depending on clinical features, disease stage and genetic subgroup. Understanding myeloma genomics has undoubtedly improved prognostic biomarkers. However, this has been slower to translate into targeted therapies compared to other cancers, and in 2023 most patients are treated with similar combination regimens initially, regardless of disease specific features. The availability of new biomarkers of disease aggression and prognosis in the near future will likely result in a movement away from this “one-size-fits-all” approach to a more individualised treatment plan.

Clinical Presentation and Diagnosis

MM patients can present with insidious or more obvious symptoms depending on the main site of disease. Bone marrow failure, due to build up of MM cells, can present as non specific fatigue, weight loss, shortness of breath or in some cases bleeding and bruising (less typical).

Patients with vertebral tumours (plasmacytomas) or bone disease can present with back pain which can be subtle initially but typically progresses rapidly within weeks to months to radiculopathy, severe pain and mobility restriction. Hip pain can also be a presenting feature for some patients and if undetected, can progress to pathological fractures. As these symptoms are common in the general population, MM is often not initially suspected. Raising awareness of these presentations is needed to prevent disability and morbidity for patients.

The main clinical features of MM are known as CRAB features (hypercalcaemia, renal insufficiency, anaemia and bone lesions). Anaemia is not always present and can range from a normocytic mild anaemia to severe anaeamia and cytopenias. To screen for MM, serum or urine

M-protein is measured – it is essential to check serum protein electrophoresis (SPEP) and serum free light chains (SFLC) as the initial blood based screen as 10% of cases will secrete light chains only and therefore could go undetected with SPEP alone.

Urinary screening for Bence Jones

Protein is also recommended as part of the diagnostic criteria but is more commonly performed by a haematolologist or nephrologist during secondary work up. Bone marrow biopsy is the diagnostic test which assesses for percentage plasma cells and . Bone lesions will also be assessed using methods such as X-rays, positron emission tomography (PET) scans, magnetic resonance imaging (MRI) and computerized tomography (CT) scans. Table 1 shows the diagnostic criteria of MM.

Current Staging Systems

In 2005, the International Myeloma Working Group (IMWG) introduced the International Staging System (ISS) to stratify patients into three prognostic groups. The ISS does this based on the clinical levels of serum β2 microglobulin and serum albumin. In 2015, this was revised (R-ISS) to include the level of lactate dehydrogenase (LDH) and genetic risk factors assessed by fluorescence in situ hybridization (FISH), specifically high-risk cytogenetic abnormalities t(4;14), t(14;16) or del(17p). The R-ISS criteria are shown in Table 2. The incorporation of genetic risk factors was an important step for MM, and since then research has continued to uncover important genetic factors.

Treatment

MM is not treated with a single agent but rather with combinational therapy. Standard of care therapy for MM now consists of a proteasome inhibitor in combination with an immunomodulatory agent. Treatment at diagnosis is focused on getting the patient into a deep remission – measured by a reduction in serum M-protein, normalisation of the light chain ratio and reduction in the percentage of bone marrow plasma cells. Initial treatment in Ireland at present consists of one of the following National Cancer Control Programme (NCCP) approved regimens; RVD (bortezomib, lenalidomide, dexamethasone), VMP (bortezomib, melphalan, prednisone), CyBorD (cyclophosphamide, bortezomib, dexamethasone), Rd (lenalidomide, dexamethasone) or most recently D-VTD (daratumumab, bortezomib, thalidomide, dexamethasone).

Treatment choice is largely guided by patient “fitness” in terms of frailty and co-morbidities, age is a factor, but biological age is more important than numerical age. MM patients can be widely classified as either eligible for an autologous stem cell transplant (ASCT), or ineligible for an ASCT, and if eligible, will receive this following induction therapy. Patients over 75 years old are generally not eligible due to the higher risk of toxicity and the availability of effective treatments for these patients. Unfortunately, most patients eventually relapse and require further treatment once symptomatic. The choice of treatment at relapse will depend on which regimen the patient received as their previous line(s) of therapy and their initial response, cytogenetics, aggressiveness of the relapse, and again the patient’s fitness and quality of life. In Ireland, there are several NCCP approved regimens for treatment of relapsed and refractory myeloma; RVD (bortezomib, lenalidomide and dexamethasone), bortezomib and dexamethasone (VD), CyBorD/cyclophosphamide, VD (bortezomib and dexamethasone), daratumumab monotherapy, pomalidomide and dexamethasone, Kd (carfilzomib and dexamethasone), KRd (carfilzomib, lenalidomide and dexamethasone), DVd (daratumumab, bortezomib and dexamethasone), IRD (ixazomib, lenalidomide and dexamethasone), and lenalidomide and dexamethasone.

Excitingly, there are many new therapies in trial for MM, most focused on the relapsed/ refractory settings. Venetoclax, a BCL-2 inhibitor, shows promise for patients with t(11;14) and if approved will be the first targeted therapy for MM. Additionally, many new therapies targeting the bone marrow microenvironment are on the horizon. These include chimeric antigen receptor (CAR) T-cells, bispecific T cell engagers (BiTEs) and novel monoclonal antibodies.

Pathogenesis – Genetic Abnormalities

MM progression is driven by the accumulation of genetic abnormalities, as well as interplay between malignant plasma cells and the bone marrow microenvironment. Generally, disease-initiating primary genetic events will occur at pre-malignant MGUS and SMM stages and can broadly be categorised into two groups – hyperdiploid and non-hyperdiploid. Hyperdiploidy refers to extra chromosomal copies, usually trisomies, and tend to affect the odd number chromosomes 3, 5, 7, 9, 11, 15, 19 and 21. Non-hyperdiploid MM is characterised by IGH gene translocations (chromosome 14q32), most commonly t(4;14), t(6;14), t(11;14), t(14;16), and t(14;20). These result from errors during B-cell differentiation where the parts of the IGH gene rearrange.

As the disease progresses to MM, secondary genetic events accumulate. These are commonly copy number variations such as del(17p), gain(1q) and del(13q), or gene mutations in cell signalling pathways such as RAS and NF-κB. As progression continues, the process of clonal evolution may occur whereby the mutations driving the disease change over time as certain clonal cell populations are selected for, either naturally or because of treatment. In rare cases, MM may progress to a very aggressive form known as plasma cell leukaemia (PCL) which occurs when clonal plasma cells circulate in peripheral blood.

Patient Prognosis

In the last two decades, the introduction of new therapies such as proteasome inhibitors, immunomodulatory agents, and monoclonal antibodies, has undoubtedly improved patient outcome. In Ireland, the 5-year survival rate is now around 53%, doubling since the early 1990s. However, in reality, patient prognosis varies widely for each individual and this is largely because of tumour heterogeneity i.e. differences in genetic make-up each myeloma. In other words, MM is not a single disease entity but rather many different types.

As a result, patients may be described as either ‘standard-risk’ or ‘high-risk’. Generally, standardrisk patients have a median survival of 7-10 years whilst high-risk patients have a much poorer prognosis of only 3 years.1 Scientific research has aimed to find ways to stratify patients accordingly but cytogenetic abnormalities determined by FISH remain the most common method. According to the Mayo Clinic Risk Stratification for Multiple Myeloma (mSMART), presence of trisomies, t(11;14) or t(6;14) confer standard-risk, whilst presence of t(4;14), t(14;16), t(14;20), del(17p) or gain(1q) is considered high-risk. Moreover, prognosis worsens even more with the presence of two high-risk factors (double hit myeloma), and again if three or more are present (triple hit myeloma). Unfortunately, across different clinical sites, there is often variation in which abnormalities are tested for, or the FISH probes used for detection. As research advances, more prognostic methods are continually being uncovered, such as the use of gene expression profiling for riskstratification, and the presence of minimal residual disease.

Gene Expression Profiling

Genomic testing in the form of gene expression profiling (GEP) has become increasingly popular, with the identification of many gene signatures that can accurately identify molecular subgroups of MM patients and predict prognosis. To date, two gene signatures have been commercialised – the MyPRS® which detects a 70-gene signature known as UAMS-70, and the MMProfiler™ which detects a 92-gene signature known as EMC92/SKY92. Both are commonly incorporated into ongoing clinical trials and have proved to successfully identify high-risk patients. However, the MMProfiler™ is currently the only GEP test with a CE-IVD (in vitro diagnostic) approval meaning it meets European standards to be used in a clinical setting. The MMprofiler™ works by determining the expression of 92 genes in myeloma plasma cells from patient bone marrow. Dependent on the way these genes are collectively expressed, a score is calculated and anything equal or above 0.827 is considered high-risk with a predicted survival of less than 2 years.2 Several studies have shown that using MMProfiler™ can overcome the need for FISH and in fact provide additional information often missed by FISH. The MMProfiler™ is already used in private healthcare settings in the UK, and in several NHS clinical trials. We are currently investigating its use here in Ireland and hope that it will lead to its routine diagnostic use. Several trials are also investigating whether it can predict treatment response, with preliminary results showing it can aid clinical decision making to escalate or deescalate treatment (PROMMIS trial, NCT02911571).

Minimal Residual Disease

Minimal residual disease (MRD) refers to the low level of cancerous cells that may persist even in patients who have shown a ‘complete response’ to treatment (reduction of M-protein and less than 5% bone marrow plasma cells). MRD is not detected using conventional morphological and serological tests and therefore tests that are more sensitive have been developed. The IMWG recommend that MRD tests reach a sensitivity level of 10-5, meaning that one malignant cell can be detected among 100,000 healthy cells, but recent detection methods report sensitivities of 106, and even 10-7.

Extensive studies show that MRD positivity is associated with inferior progression free survival and overall survival compared to MRD negativity, and in some cases may even overcome cytogenetic risk factors. For example, patients presenting with highrisk cytogenetics (4;14), t(14;16), or del(17p) who reached MRD negativity had a better outcome than standard-risk patients who were MRD positive.3 Alternatively, high-risk patients who are MRD positive exhibited the worst prognosis, highlighting the prognostic potential of assessing both factors in combination.

Unfortunately, the most common methods used for MRD detection also lack sensitivity and standardisation. Multiparameter flow cytometry is most common, which works by immunophenotyping cells by detecting and quantifying cell-surface proteins associated with malignant MM cells. Like with FISH, this method can vary between clinical sites, with discrepancies in markers used, different antibodies for detection, and varying analysis methods to name a few. Great efforts have been made to standardise flow cytometry, and now next generation flow (NGF) has been approved by the IMWG. NGF was developed by the EuroFlow consortium and comprises of an eight-colour flow assay that allows the simultaneous analysis of up to 10 million cells. However, there are still limitations associated with NGF, the main one being the need for fresh samples and immediate processing. As a result, molecular genomic-based MRD tests are an attractive alternative, since DNA can be preserved and stored for later analysis.

Next-generation sequencing (NGS) techniques have been developed for MRD detection. These look for clonal DNA sequences within immunoglobulin genes, usually the IGH gene, which occur during a process known as V(D) J recombination.4 This is the rearrangement of DNA regions known as Variable (V), Diversity (D) and Joining (J) regions which is necessary to ensure production of antibodies. However, in MM this process is dysregulated resulting in clonal DNA rearrangements, and production of M-protein instead. There are two commercialised, standardised tests designed to detect these rearrangements – Adaptive’s ClonoSEQ® and Invivoscribe’s LymphoTrack®. Both of these detect the clonal diseasedriving sequence at diagnosis, and determine if it remains in follow-up samples. The main limitation here is that a diagnostic sample is required, which is not always available. Moreover, to ensure cost effectiveness it is better to run large numbers of samples simultaneously, which may not always be feasible. Despite these, ClonoSEQ® is the only NGS method FDA approved and reports a sensitivity of up to 10-7. However, it is not commercially available which limits its use in many centres due to expense. On the other hand, LymphoTrack® can be performed in laboratories in-house and thus is a more feasible choice for most researchers. As research continues into the benefits of using MRD as a prognostic test, the hope is that it may spare patients from particularly toxic, aggressive therapies where the risk of relapse outweighs any potential benefit.

Spatial Heterogeneity

As mentioned, the accumulation of MM cells in the bone marrow results in focal lesions, which can be visualised using imaging techniques such as PET scans. Bone marrow biopsies taken for testing are usually from the posterior iliac crest meaning any genetic tests performed are from one specific location and give us a ‘snapshot’ rather than the whole picture. However, recent research has shown that myeloma heterogeneity can occur across different focal lesions within the same patient, in other words, spatial heterogeneity. For example, a patient may present as standardrisk at both cytogenetic or GEP level of iliac crest bone marrow, but high-risk when the same tests are performed on plasma cells from a focal lesion elsewhere.5 Therefore, to understand exactly how each individual’s disease is behaving it may be beneficial to perform genomic sequencing at several disease sites. Of course, however, bone marrow biopsies are very invasive and so in reality this would be difficult to introduce routinely. Both the number and size of focal lesions also correlates with disease severity, and so it is advised that imaging is also used for MRD monitoring. As we learn more about spatial heterogeneity, this may also become a consideration when monitoring MRD using NGS methods, as V(D) J rearrangements may also differ between lesions.

Extramedullary disease

Around 20% of patients will present with extramedullary disease (EMD), which occurs when MM cells infiltrate other organ systems, becoming independent of the bone marrow microenvironment. This is a particularly aggressive form of MM and largely unresponsive to current therapies, and may present at diagnosis or at relapse. Moreover, EMD is a poor prognostic factor with an overall survival rate of only 6 months.6 EMD is associated with both high-risk cytogenetics and high-risk MM as defined by GEP-70. Moreover, these patients rarely present with standard-risk abnormality t(11;14). More recently, a link between EMD and highrisk chromosome 1 abnormalities has also been reported.7 Very few studies have investigated the genomic landscape of EMD, but those that have revealed mutations in tumour-driving RAS signalling pathways. With these early studies already suggesting a high prevalence of various high-risk markers in EMD, it is necessary that we learn more about the genomic landscape of EMD to improve outcomes for this poor prognostic group.

Future Implications

MM outcome is continually improving due to discovery of novel therapies and understanding of disease biology. By using the genomic tools such as those we have discussed, we hope that in the future this will ultimately translate into more targeted therapies for each MM patient.

Using NGS tools to predict prognosis such as GEP and MRD detection will enable us to better characterise how genetic subgroups perform over time and respond to therapies. Moreover, understanding how gene signatures drive disease biology may uncover novel therapeutic targets. Future research should also aim to understand the role of spatial heterogeneity and EMD in patient prognosis.