Since the body has many different types of plasma cells, it can respond to, or fight against, many different foreign substances. When plasma cells become cancerous, they reproduce uncontrollably. The tremendously increased number of plasma cells in multiple myleoma crowd out healthy red and white blood cells, preventing them from functioning as effectively as they should. The malignant plasma cells produce osteoclast activating factors which cause calcium to be leached out of the bones. This leaching of calcium can result in dangerously high levels of calcium in the bloodstream, known as hypercalcemia, and holes in bones, known as osteolytic lesions.
Some patients experience vertebral collapse or spontaneous fractures.
The malignant plasma cells also produce excessive monoclonal immunoglobulin, a type of protein, referred to as an M-protein. This protein can overload the kidneys, leading to abnormal kidney function and even renal failure. Sometimes malignant plasma cells congregate in clumps, causing isolated tumors, or plasmacytomas. Early myeloma may cause no overt symptoms, but as tumor mass increases and excess protein is produced, symptomatic disease develops. Typical symptoms include bone pain, anemia, and renal failure.