Like all components of blood, plasma cells are produced in the bone marrow.
Plasma cells produce proteins that help protect the body from infection.
After one or more of these cells becomes cancerous, they multiply rapidly. The proteins these cancerous cells make do not work as well as normal proteins. The cancerous cells produce very large amounts of the faulty proteins. These cancerous cells may also crowd out normal cells. Some of the cancerous plasma cells will leave the bone marrow and enter the bloodstream.