5. Multiple Myeloma

What is multiple myeloma?

Multiple myeloma is the only type of cancer that develops from plasma cells. Plasma cells normally produce antibodies to combat infection, and plasma cells themselves develop from B-cells, in response to infection. B-cells are a type of lymphocyte in lymph nodes and other lymphatic tissue. B-cells develop from lymphoid stem cells in the bone marrow before they move to lymphatic tissue. Multiple myeloma can thus arise when there’s a mutation in a lymphoid stem cell that causes the cells to mature all the way to being plasma cells without ever leaving the bone marrow and without needing an infection to fight.

How is multiple myeloma similar to leukemia?

Multiple myeloma is similar to lymphoid leukemias in that both develop from lymphoid cells. Multiple myeloma is similar to chronic leukemias in that the cancerous cells in both can mature. Symptoms related to cancerous cells taking up space in the bone marrow and preventing production of normal blood cells are in common between multiple myeloma and some leukemias – these symptoms include anemia, susceptibility to infection, bleeding and bruising.

How is multiple myeloma different from leukemia?

Multiple myeloma is not a type of leukemia; it’s in a distinct category of its own. Unlike cancerous cells in leukemias, cancerous plasma cells are much more trapped in the bone marrow – almost ALL cancer cells in multiple myeloma stay in the bone marrow, so the cancer cells can almost never be detected in the blood. In contrast, in leukemia enough cancer cells usually escape into the blood to be detectable in the blood.  The cancerous plasma cells in multiple myeloma may be particularly well trapped in the bone marrow because cells don’t usually mature into plasma cells until they’re already out of the bone marrow – thus plasma cells haven’t needed to develop a way of getting out.

What are symptoms unique to multiple myeloma?

Multiple myeloma is distinct in that the cancerous plasma cells tend to eat into the bone around them, causing bones to break more easily. Eating away at bone also releases into the blood the chemicals that the bone was made of, including calcium. Increased calcium in the blood can cause additional symptoms. Multiple myeloma is also unique in that it produces antibodies – I’ve mentioned plasma cells normally make antibodies, which are proteins that can stick specifically to parts of invading organisms. Cancerous plasma cells still make antibodies – in fact they can make very large amounts of a single type of antibody. These antibodies, called IgG or IgM and detected by a lab test called serum protein electrophoresis, can get stuck in your kidneys. Since kidneys remove waste from the blood and allow that waste to be excreted as part of urine, kidney problems can affect urine production and the removal of waste from the body.  Most other blood cancers do not produce antibodies, so don’t have these complications

References

Leukemia and Lymphoma Society of Canada. Disease and Support Information. July 11 2013. Available at http://www.llscanada.org/?gclid=COr5jbK34roCFQVgMgodfl4AMQ#/diseaseinformation/. Accessed Nov 2013.

Aster JC. Chapter 24. Multiple Myeloma and Related Disorders. In: Bunn H, Aster JC. eds. Pathophysiology of Blood DisordersNew York: McGraw-Hill; 2011.http://accessmedicine.mhmedical.com.ezproxy.library.ubc.ca/content.aspx?bookid=676&Sectionid=44827794. Accessed February 09, 2014.

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