Multiple myeloma tends to spread through the blood in the form of monoclonal protein. It is found most commonly in the bone marrow and bones, but it can affect the kidneys and immune system. Occasionally, a collection of plasma cells (myeloma cells) may collect in an organ/soft tissue. This is called a plasmacytoma. Here are some of the most common skeletal areas that may be affected by myeloma cells:
In rare cases when multiple myeloma spreads outside of the bones, it may go to the soft tissues of the body. However, even when myeloma stays in the bone marrow, myeloma cells make an abnormal protein that travels throughout the body and can damage other organs such as the kidneys.