Myeloma usually grows inside the bone marrow. Bone marrow tests (aspirate and biopsy) are performed routinely to diagnose multiple myeloma and are also used for periodic monitoring during the course of treatment. A bone marrow biopsy provides information about the amount of disease, its aggressiveness, and molecular/genetic abnormalities that help to predict the disease course. Bone marrow biopsies are necessary because they provide the only direct access to tumor cells for examination by a pathologist. However, because myeloma is patchy and is not distributed evenly throughout the bone marrow, such biopsies do not always present an accurate sample of what is occurring elsewhere in the marrow.
Other tissue biopsies are performed less frequently to determine if myeloma is present outside the bone marrow. A biopsy may also be performed in early-stage disease on a solitary plasmacytoma.
Bone Marrow Aspiration and Core Biopsy
Bone marrow aspiration and bone marrow core biopsy are methods to collect both the liquid and solid parts of the bone marrow. Aspiration is done with a syringe that draws out the liquid part of the marrow; core biopsy is done with a special hollow needle to capture a sample of the spongy bone in the marrow along with its contents. Bone marrow aspiration and core biopsy may be uncomfortable or painful, but must be performed because they provide samples for the only direct means of examining the myeloma cells under a microscope. All other tests (of the blood and urine) rely on indirect markers of what myeloma cells are doing. The pathologist who looks at the actual cells writes a report detailing how many of the cells in the sample are abnormal plasma cells and what they look like. Words like mature, immature, and atypical may appear in your report.
The following tests are then performed on the samples collected through aspiration and core biopsy.
Immunophenotyping is done by flow cytometry to identify protein markers on the surface of myeloma cells. Immunophenotyping is used to determine both stringent complete response (sCR) and minimal residual disease (MRD), which indicates a near total eradication of myeloma cells.
The Next Generation Flow cytometry test was developed and funded by the IMF Black Swan Research Initiative to detect minimal residual disease. NGF is sensitive enough to detect one myeloma cell among every one million plasma cells sampled from the bone marrow.
Cytogenetics, also known as Karyotyping
Standard cytogenetics (karyotyping) is the assessment of the chromosomes in a cell's nucleus during cell division. Cytogenetics is also called karyotyping because a karyotype is the number and appearance of chromosomes in a cell's nucleus.
This test is routinely performed on the bone marrow of newly diagnosed myeloma patients and is sometimes repeated after treatment, especially after high-dose therapy with stem cell rescue (autologous stem cell transplant). Cytogenetics testing is performed along with FISH (discussed next), mainly to determine if there is loss of chromosome 13 during myeloma cell division. Loss of chromosome 13 can be detected better with cytogenetics than with FISH. Loss of chromosome 13 is usually an indication that other genetic abnormalities are present in the myeloma cells.
Fluorescence In-Situ Hybridisation (FISH)
FISH provides a way to map the genetic material, including genes and portions of genes, found in the myeloma cells. This helps us understand a variety of genetic mutations that indicate a patient’s risk status.
FISH demonstrates the movement of genetic material from one chromosome to another (translocations) and/or the absence of genetic material on chromosomes (deletions). Certain deletions and translocations are known to be signs of myeloma that is more aggressive (high-risk multiple myeloma). These high-risk mutations include the following:
- Translocation (4;14), which is movement of gene segments from chromosome 4 to 14.
- Deletion 17p, which is the loss of the short arm (top part) of chromosome 17, which is where a major tumor suppressor gene (the p53 gene) is located..
- Translocation (14;16), which is movement of gene segments from chromosomes 14 to 16.
- 1q+, which is the addition of an extra long arm (bottom part) of chromosome 1.
Gene Expression Profiling (GEP)
GEP is performed on RNA extracted from myeloma cells. The genes present in the RNA are then probed on a special computer chip to provide a global picture of disease biology. GEP is used to identify the dominant clone at any particular time in a patient’s disease course and to classify myeloma into different molecular subgroups, buts its most important function has been to identify the gene expression profile of patients with high-risk myeloma.
GEP does not provide information about non-dominant disease clones or about “driver” genetic mutations that allow the myeloma to grow and develop in new areas of the body. Different institutions have developed different GEP high-risk expression profiles that have not yet been standardized. GEP is not widely available.