Bone marrow cancer. Light micrograph of a bone marrow cancer, myeloma. Cancerous cells (purple, darker staining) have replaced most of the healthy tissue, leaving a patch of dying normal cells (pink). Myeloma is a cancer of plasma cells (antibody-producing cells found in 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. The myeloma cells replace normal cells needed for immune response and blood clotting. They may also make an abnormal antibody which interferes with normal antibody production. Magnification unknown.