Bone marrow cancer. Coloured X-ray of the head of the humerus (upper arm bone) being invaded by a tumour (orange). This is an example of myeloma, a cancer of plasma cells (antibody-producing white blood cells) which originates in the bone marrow. The cells may spread throughout the body, causing multiple tumours. As well as damaging bones, myeloma can cause anaemia and reduce the ability of the body to fight infection. This is because the myeloma cells fill the bone marrow, replacing normal cells needed for immune response and blood clotting. They may also make an abnormal antibody which interferes with normal antibody production.