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Scientists still do not know exactly what causes most cases of
multiple myeloma. However, they have made progress in understanding how
certain changes in DNA can cause plasma cells to become cancerous. DNA
is the chemical that carries the instructions for nearly everything our
cells do. Some genes
(parts of our DNA) contain instructions for controlling when our cells
grow and divide. Certain genes that promote cell division are called oncogenes. Others
that slow down cell division or cause cells to die at the appropriate
time are called tumor
suppressor genes. Cancers can be caused by mistakes, or
defects, in the DNA called mutations
that turn on oncogenes or turn off tumor suppressor genes.
Recent studies have found that abnormalities of some oncogenes
(such as c-myc) develop early in the course of plasma cell tumors.
Changes in other oncogenes (such as N-ras and K-ra) are more often
found in myeloma after bone marrow relapse, and changes in tumor
suppressor genes (such as p53) are associated with spread to other
organs.
Myeloma cells also show abnormalities in their chromosomes.
Normal human cells contain 46 chromosomes--pieces of DNA and protein
that control cell growth and metabolism. One fairly common finding in
myeloma cells is that parts of chromosome number 13 are missing. These
deletions appear to make the myeloma more aggressive and resistant to
treatment.
About half of all people with myeloma have abnormally
translocated chromosomes in their myeloma cells. This means that a part
of one chromosome has switched with part of another chromosome. This
often occurs in a crucial area next to an oncogene, which causes it to
be turned on.
Researchers have found that patients with plasma cell tumors
have important abnormalities in other bone marrow cells and that these
abnormalities may also cause excess plasma cell growth. Certain cells
in the bone marrow called dendritic
cells release a hormone called interleukin-6 (IL-6), which
stimulates normal plasma cells to grow. Excess IL-6 production by these
cells appears to be an important factor in development of plasma cell
tumors.
Last Medical Review: 02/13/2009
Last Revised: 05/12/2009
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