Illustration of chimeric antigen receptor (CAR) T cells (blue) attacking multiple myeloma cells (purple). Multiple myeloma is type of cancer, it occurs when a plasma cell becomes abnormal and cancerous. The cancerous plasma cell divides and multiplies creating large amounts of abnormal antibodies. CAR-T therapy is a type of immunotherapy that genetically modifies a patients own T cells, a form of white blood cell, to recognise and destroy cancer cells.