Bone cancer. Light micrograph of a section through bone marrow affected by multiple myeloma (Kahlers disease), showing a proliferation of plasma cells. Multiple myeloma is a cancer arising from plasma cells, a form of white blood cell normally responsible for producing antibodies. In this condition, large numbers of abnormal plasma cells accumulate in the bone marrow, where they interfere with the production of normal blood cells. Bone lesions may develop, causing the bone to weaken and become vulnerable to fractures. Multiple myeloma is not curable, but can be treated with steroids, chemotherapy and stem cell transplants. Magnification: x1111, when printed 10 centimetres wide.