Multiple Myeloma is a cancer that affects the bone marrow where the cells in our blood system are formed. This includes the white cells, red cells, platelets and lymphoid cells. In multiple myeloma the plasma cell (one of the lymphoid cells) starts to reproduce out of control. This results in crowding of the bone marrow with abnormal production of all the cells and a malfunction of the plasma cells. They can also cause damage to the normal bone resulting in pain, fractures and other complications.