Multiple myeloma is a cancer that forms in plasma cells, a type of white blood cell found in the bone marrow. When these cells become cancerous, they multiply uncontrollably, crowding out healthy blood cells. To analyze these cells, doctors use a laboratory test called flow cytometry. This technology allows for a detailed examination of individual cells, helping to identify and characterize the cancerous plasma cells with a high degree of precision for managing the disease.
The Purpose of Flow Cytometry in Multiple Myeloma
Flow cytometry is a laboratory method used for the diagnosis, risk assessment, and monitoring of multiple myeloma. Its primary diagnostic function is to distinguish between normal plasma cells and their malignant counterparts by detecting specific proteins on the cell surface. This process helps confirm that a plasma cell population is clonal, meaning it originates from a single cancerous cell.
The information gathered also aids in determining the disease’s prognosis. The specific characteristics of the myeloma cells, such as the presence or absence of certain surface proteins, can indicate a more or less aggressive form of cancer. This risk stratification allows medical professionals to tailor treatment strategies.
Flow cytometry is also used to monitor treatment effectiveness by quantifying cancerous plasma cells. A significant reduction in malignant cells indicates a treatment is working. A stable or increasing number may signal a need to adjust the therapeutic approach.
The Flow Cytometry Process Explained
The flow cytometry process begins with obtaining a sample, typically from a bone marrow aspirate or peripheral blood. This sample contains a mixture of cells, which are then suspended in a fluid to prepare them for individual analysis.
Before the analysis, the cells are treated with specific antibodies tagged with fluorescent dyes. These antibodies are designed to recognize and bind to unique proteins, or markers, on the surface of cells like CD38 and CD138, which are abundant on plasma cells.
The prepared sample is then injected into the flow cytometer, where the fluid carries the cells in a single file stream through a laser beam. As each cell passes through the laser, the fluorescent dyes attached to it emit light. Detectors capture this light, providing information about the cell’s size, complexity, and the specific markers it carries for precise characterization.
Measuring Minimal Residual Disease
A significant application of flow cytometry in multiple myeloma is the measurement of minimal residual disease (MRD). MRD describes the small number of cancer cells that can remain in the body after treatment, even when a patient shows no signs of the disease by conventional assessments. These lingering cells are often the source of relapse, making their detection a focus of modern myeloma care.
Flow cytometry is exceptionally sensitive, capable of detecting as few as one cancer cell among a million or more healthy cells. This high level of sensitivity is achieved through techniques often called next-generation flow (NGF). This provides a very precise measurement of any remaining myeloma cells.
The results of an MRD test have direct implications for patient management. An “MRD-negative” result indicates that no cancer cells were detected at the specified level of sensitivity and is strongly associated with longer periods of remission. Conversely, an “MRD-positive” result means that a small number of myeloma cells are still present, which can prompt doctors to consider additional treatment or more frequent monitoring.
How Flow Cytometry Complements Other Myeloma Tests
Flow cytometry is one piece of a comprehensive diagnostic puzzle and its findings are interpreted alongside other medical tests. A bone marrow biopsy is a standard procedure where a pathologist examines a sample of bone marrow under a microscope. While this shows the overall percentage of plasma cells and their physical arrangement, flow cytometry provides a deeper layer of information by identifying the specific surface markers that confirm their cancerous nature.
Blood and urine tests, such as serum protein electrophoresis (SPEP), measure the amount of abnormal M-protein produced by the myeloma cells. A decrease in M-protein is a good indicator of treatment response, but flow cytometry directly measures the cancer cells themselves, which can be a more sensitive approach, particularly when M-protein levels are low.
Imaging techniques like PET scans and MRIs play a different role by visualizing the impact of the disease on the body. These scans are used to locate bone damage or tumors called plasmacytomas. While imaging shows the structural consequences of myeloma, flow cytometry analyzes the disease at a microscopic, cellular level.