Definition of Multiple Myeloma

Multiple Myeloma Definition

Multiple myeloma is form of blood cancer that develops in the bone marrow. In multiple myeloma, normal plasma cells transform into malignant myeloma cells and produce large quantities of an abnormal immunoglobulin called monoclonal protein or M protein. The monoclonal protein produced by myeloma cells, interferes with normal blood cell production. In addition, the levels of functional immunoglobulins are depressed in individuals with multiple myeloma. Although the process is not completely understood, it appears that the functional immunoglobulins made by existing, healthy plasma cells breaks down more quickly in patients with multiple myeloma than in healthy individuals.

How normal plasma cells develop

Plasma cells are one of many types of blood cells that arise from stem cells in the bone marrow. Plasma cells develop from B lymphocytes (also known as B cells), which are a major class of white blood cells, the blood cells that fight infection in the body. Normally, plasma cells make up about 5% of all cells in the bone marrow.

Plasma cells develop from B cells when foreign substances (antigens), such as bacteria, enter the body. In response to an invasion by foreign substances, groups of plasma cells produce immunoglobulins (also known as antibodies) that help fight off disease and infection caused by the foreign substance. Each plasma cell develops in response to a particular foreign substance within the body and produces immunoglobulins specific to that substance. As a result, many different immunoglobulins are produced in the body.

How Plasma Cells Transform Into Myeloma Cells

Normal plasma cells (B cells) transform into malignant plasma cells (myeloma cells) through a multistep process.

The process begins when specific adhesion molecules on the surface of myeloma cells allow the cells to bind to stromal cells in the bone marrow. This attachment allows both the stromal cells and the myeloma cells to produce chemical messengers called cytokines that cause the further development of myeloma.

  • Stromal cells produce an increased amount of the cytokine interleukin-6 (IL-6), which is necessary for the continued growth and survival of the myeloma cells. The high level of IL-6 leads to an uncontrolled increase in the number of myeloma cells.
  • Myeloma cells produce an increased amount of IL-1-beta and tumor necrosis factor-beta (TNF-beta), two cytokines that activate the development of osteoclasts, cells that break down bone as part of normal bone remodeling. However, in multiple myeloma, the increased number of osteoclasts causes damage to bone.
  • Myeloma cells also produce growth factors, such as vascular endothelial growth factor (VEGF), that promote angiogenesis, or the creation of new blood vessels. These new blood vessels bring oxygen and nutrients to the tumor, helping it to grow by generating new myeloma cells.
  • Mature myeloma cells may fail to activate the immune system, which means that the body’s immune system will not respond to a foreign substance. This failure results in a growing number of myeloma cells.