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Multiple myeloma

Multiple myeloma (also known as MM, myeloma, plasma cell myeloma, or as Kahler's disease after Otto Kahler) is a type of cancer of plasma cells which are immune system cells in bone marrow that produce antibodies. Myeloma is regarded as incurable, but remissions may be induced with steroids, chemotherapy, thalidomide and stem cell transplants. Myeloma is part of the broad group of diseases called hematological malignancies.

Signs and symptoms

Because many organs can be affected by myeloma, the symptoms and signs vary greatly. A mnemonic sometimes used to remember the common tetrad of multiple myeloma is CRAB - C = Calcium (elevated), R = Renal failure, A = Anemia, B = Bone lesions. Myeloma has many possible symptoms, and all symptoms may be due to other causes. They are presented here in decreasing order of incidence.

Bone pain

Myeloma bone pain usually involves the spine and ribs, and worsens with activity. Persistent localized pain may indicate a pathological bone fracture. Involvement of the vertebrae may lead to spinal cord compression. Myeloma bone disease is due to proliferation of tumor cells and release of IL-6, also known as osteoclast activating factor (OAF), which stimulates osteoclasts to break down bone. These bone lesions are lytic in nature and are best seen in plain radiographs, which may show "punched-out" resorptive lesions. The breakdown of bone also leads to release of calcium into the blood, leading to hypercalcemia and its associated symptoms.

Infection

The most common infections are pneumonias and pyelonephritis. Common pneumonia pathogens include S. pneumoniae, S. aureus, and K. pneumoniae, while common pathogens causing pyelonephritis include E. coli and other gram-negative organisms. The greatest risk period for the occurrence of infection is in the initial few months after the start of chemotherapy. The increased risk of infection is due to immune deficiency resulting from diffuse hypogammaglobulinemia, which is due to decreased production and increased destruction of normal antibodies. A selected group of patients may benefit from replacement immunoglobulin therapy to reduce the risk of infection.

Renal failure

Renal failure may develop both acutely and chronically. It is commonly due to hypercalcemia (see above). It may also be due to tubular damage from excretion of light chains, also called Bence Jones proteins, which can manifest as the Fanconi syndrome (type II renal tubular acidosis). Other causes include glomerular deposition of amyloid, hyperuricemia, recurrent infections (pyelonephritis), and local infiltration of tumor cells.

Anemia

The anemia found in myeloma is usually normocytic and normochromic. It results from the replacement of normal bone marrow by infiltrating tumor cells and inhibition of normal red blood cell production (hematopoiesis) by cytokines.

Neurological symptoms

Common problems are weakness, confusion and fatigue due to hypercalcemia. Headache, visual changes and retinopathy may be the result of hyperviscosity of the blood depending on the properties of the paraprotein. Finally, there may be radicular pain, loss of bowel or bladder control (due to involvement of spinal cord leading to cord compression) or carpal tunnel syndrome and other neuropathies (due to infiltration of peripheral nerves by amyloid). It may give rise to paraplegia in late presenting cases.

Diagnosis

Investigations

The presence of unexplained anemia, kidney dysfunction, a high erythrocyte sedimentation rate (ESR) and a high serum protein (especially raised immunoglobulin) may prompt further testing. A doctor will request protein electrophoresis of the blood and urine, which might show the presence of a paraprotein (monoclonal protein, or M protein) band, with or without reduction of the other (normal) immunoglobulins (known as immune paresis). One type of paraprotein is the Bence Jones protein which is a urinary paraprotein composed of free light chains (see below). Quantitative measurements of the paraprotein are necessary to establish a diagnosis and to monitor the disease. The paraprotein is an abnormal immunoglobulin produced by the tumor clone. Very rarely, the myeloma is nonsecretory (not producing immunoglobulins).

In theory, multiple myeloma can produce all classes of immunoglobulin, but IgG paraproteins are most common, followed by IgA and IgM. IgD and IgE myeloma are very rare. In addition, light and or heavy chains (the building blocks of antibodies) may be secreted in isolation: κ- or λ-light chains or any of the five types of heavy chains (α-, γ-, δ-, ε- or μ-heavy chains).

Additional findings include: a raised calcium (when osteoclasts are breaking down bone, releasing calcium into the bloodstream), raised serum creatinine due to reduced renal function, which may be due to paraprotein deposition in the kidney.

Workup

The workup of suspected multiple myeloma includes a skeletal survey. This is a series of X-rays of the skull, axial skeleton and proximal long bones. Myeloma activity sometimes appear as "lytic lesions" (with local disappearance of normal bone due to resorption), and on the skull X-ray as "punched-out lesions" (pepper pot skull). Magnetic resonance imaging (MRI) is more sensitive than simple X-ray in the detection of lytic lesions, and may supersede skeletal survey, especially when vertebral disease is suspected. Occasionally a CT scan is performed to measure the size of soft tissue plasmacytomas. Bone scans are typically not of any additional value in the workup of myeloma patients.

A bone marrow biopsy is usually performed to estimate the percentage of bone marrow occupied by plasma cells. This percentage is used in the diagnostic criteria for myeloma. Immunohistochemistry (staining particular cell types using antibodies against surface proteins) can detect plasma cells which express immunoglobulin in the cytoplasm but usually not on the surface; myeloma cells are typically CD56, CD38, CD138 positive and CD19 and CD45 negative. Cytogenetics may also be performed in myeloma for prognostic purposes.

Other useful laboratory tests include quantitative measurement of IgA, IgG, IgM (immunoglobulins) to look for immune paresis, and β2-microglobulin which provides prognostic information. On peripheral blood smear the rouleaux formation of red blood cells is commonly seen.

The recent introduction of a commercial immunoassay for measurement of free light chains potentially offers an improvement in monitoring disease progression and response to treatment, particularly where the paraprotein is difficult to measure accurately by electrophoresis (for example in light chain myeloma, or where the paraprotein level is very low). Initial research also suggests that measurement of free light chains may also be used, in conjunction with other markers, for assessment of the risk of progression from monoclonal gammopathy of undetermined significance (MGUS) to multiple myeloma.

Diagnostic criteria

In 2003, the International Myeloma Working Group agreed on diagnostic criteria for symptomatic myeloma, asymptomatic myeloma and MGUS (monoclonal gammopathy of undetermined significance):

  • Symptomatic myeloma:
    1. Clonal plasma cells >10% on bone marrow biopsy or (in any quantity) in a biopsy from other tissues (plasmacytoma)
    2. A monoclonal protein (paraprotein) in either serum or urine
    3. Evidence of end-organ damage (related organ or tissue impairment, ROTI):
  • Asymptomatic myeloma:
    1. Serum paraprotein >30 g/L AND/OR
    2. Clonal plasma cells >10% on bone marrow biopsy AND
    3. NO myeloma-related organ or tissue impairment
  • Monoclonal gammopathy of undetermined significance (MGUS):
    1. Serum paraprotein <30 g/L AND
    2. Clonal plasma cells <10% on bone marrow biopsy AND
    3. NO myeloma-related organ or tissue impairment

Related conditions include solitary plasmacytoma (a single tumor of plasma cells, typically treated with irradiation), plasma cell dyscrasia (where only the antibodies produce symptoms, e.g. AL amyloidosis), and POEMS syndrome (peripheral neuropathy, organomegaly, endocrinopathy, monoclonal plasma cell disorder, skin changes).

Staging

International Staging System The International Staging System (ISS) for myeloma was published by the International Myeloma Working Group in 2005:

  • Stage I: β2-microglobulin (β2M) < 3.5 mg/L, albumin >= 3.5 g/dL
  • Stage II: β2M < 3.5 and albumin < 3.5; or β2M >= 3.5 and < 5.5
  • Stage III: β2M >= 5.5Durie-Salmon staging system

First published in 1975, the Durie-Salmon staging system is still in use, but has largely been superseded by the simpler ISS:

  • stage 1: all of
    • Hb > 10g/dL
    • normal calcium
    • Skeletal survey: normal or single plasmacytoma or osteoporosis
    • Serum paraprotein level < 5 g/dL if IgG, < 3 g/dL if IgA
    • Urinary light chain excretion < 4 g/24h
  • stage 2: fulfilling the criteria of neither 1 nor 3
  • stage 3: one or more of
    • Hb < 8.5g/dL
    • high calcium > 12mg/dL
    • Skeletal survey: 3 or more lytic bone lesions
    • Serum paraprotein >7g/dL if IgG, > 5 g/dL if IgA
    • Urinary light chain excretion > 12g/24h

Stages 1, 2 and 3 of the Durie-Salmon staging system can be divided into A or B depending on serum creatinine:

  • A: serum creatinine < 2mg/dL (< 177 umol/L)
  • B: serum creatinine > 2mg/dL (> 177 umol/L)

Pathophysiology

Multiple myeloma develops in post-germinal center B lymphocytes. A chromosomal translocation between the immunoglobulin heavy chain gene (on the fourteenth chromosome, locus 14q32) and an oncogene (often 11q13, 4p16.3, 6p21, 16q23 and 20q11) is frequently observed in patients with multiple myeloma. This mutation results in dysregulation of the oncogene which is thought to be an important initiating event in the pathogenesis of myeloma. The result is proliferation of a plasma cell clone and genomic instability that leads to further mutations and translocations. The chromosome 14 abnormality is observed in about 50% of all cases of myeloma. Deletion of (parts of) the thirteenth chromosome is also observed in about 50% of cases.

Production of cytokines (especially IL-6) by the plasma cells causes much of their localised damage, such as osteoporosis, and creates a microenvironment in which the malignant cells thrive. Angiogenesis (the attraction of new blood vessels) is increased.

The produced antibodies are deposited in various organs, leading to renal failure, polyneuropathy and various other myeloma-associated symptoms.

Treatment

Treatment for multiple myeloma is focused on disease containment and suppression. If the disease is completely asymptomatic (i.e. there is a paraprotein and an abnormal bone marrow population but no end-organ damage), treatment may be deferred.

In addition to direct treatment of the plasma cell proliferation, bisphosphonates (e.g. pamidronate or zoledronic acid) are routinely administered to prevent fractures and erythropoietin to treat anemia.

Initial therapy

Initial treatment of multiple myeloma depends on the patient’s age and comorbidities. In recent years, high-dose chemotherapy with hematopoietic stem-cell transplantation has become the preferred treatment for patients under the age of 65. Prior to stem-cell transplantation, these patients receive an initial course of induction chemotherapy. The most common induction regimens used today are thalidomidedexamethasone, bortezomib based regimens, and lenalidomide–dexamethasone. Autologous stem cell transplantation, the transplantation of a patient’s own stem cells after chemotherapy, is the most common type of stem cell transplantation for multiple myeloma. It is not curative, but does prolong overall survival. Allogeneic stem cell transplantation, the transplantation of a healthy person’s stem cells into the affected patient, has the potential for a cure, but is only available to a small percentage of patients. Furthermore, there is a 5-10% treatment-associated mortality rate.

Patients over age 65 and patients with significant concurrent illness often cannot tolerate stem cell transplantation. For these patients, the standard of care has been chemotherapy with melphalan and prednisone. Recent studies among this population suggest improved outcomes with new chemotherapy regimens. Treatment with bortezomib, melphalan and prednisone had an estimated overall survival of 83% at 30 months, lenalidomide plus low-dose dexamethasone an 82% survival at 2 years and melphalan, prednisone and lenalidomide had a 90% survival at 2 years. Head-to-head studies comparing these regimens have not been performed.

Relapse

The natural history of myeloma is of relapse following treatment. Depending on the patient's condition, the prior treatment modalities used and the duration of remission, options for relapsed disease include re-treatment with the original agent, use of other agents (such as melphalan, cyclophosphamide, thalidomide or dexamethasone, alone or in combination), and a second autologous stem cell transplant.

Later in the course of the disease, "treatment resistance" occurs. This may be a reversible effect, and some new treatment modalities may re-sensitize the tumor to standard therapy. For patients with relapsed disease, bortezomib (or Velcade) is a recent addition to the therapeutic arsenal, especially as second line therapy, since 2005. Bortezomib is a proteasome inhibitor. Finally, lenalidomide (or Revlimid), a less toxic thalidomide analog, is showing promise for treating myeloma.

Renal failure in multiple myeloma can be acute (reversible) or chronic (irreversible). Acute renal failure typically resolves when the calcium and paraprotein levels are brought under control. Treatment of chronic renal failure is dependent on the type of renal failure and may involve dialysis.

Prognosis

The International Staging System can help to predict survival, with a median survival of 62 months for stage 1 disease, 45 months for stage 2 disease, and 29 months for stage 3 disease.

Cytogenetic analysis of myeloma cells may be of prognostic value, with deletion of chromosome 13, non-hyperdiploidy and the balanced translocations t(4;14) and t(14;16) conferring a poorer prognosis. The 11q13 and 6p21 cytogenetic abnormalities are associated with a better prognosis.

Prognostic markers such as these are always generated by retrospective analyses, and it is likely that new treatment developments will improve the outlook for those with traditionally "poor-risk" disease.

Epidemiology

There are approximately 45,000 people in the United States living with multiple myeloma, and the American Cancer Society estimates that approximately 14,600 new cases of myeloma are diagnosed each year in the United States. It follows from here that the average survival at diagnosis is about three years.

Multiple myeloma is the second most prevalent blood cancer (10%) after non-Hodgkin's lymphoma. It represents approximately 1% of all cancers and 2% of all cancer deaths. Although the peak age of onset of multiple myeloma is 65 to 70 years of age, recent statistics indicate both increasing incidence and earlier age of onset.

Multiple myeloma affects slightly more men than women. African Americans and Native Pacific Islanders have the highest reported incidence of this disease in the United States and Asians the lowest. Results of a recent study found the incidence of myeloma to be 9.5 cases per 100,000 African Americans and 4.1 cases per 100,000 Caucasian Americans. Among African Americans, myeloma is one of the top 10 leading causes of cancer death.

See also

References

External links

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