Multiple myeloma is a cancer of plasma cells that produces monoclonal proteins. It often involves bones, causing pain and fractures. Other clinical features include infection due to low antibodies, renal failure from protein deposits or hypercalcemia, and anemia. Diagnosis requires bone marrow plasma cells over 10% or monoclonal proteins plus CRAB features. Treatment depends on staging and age, including chemotherapy, steroids, stem cell transplant, or supportive care. Amyloidosis involves the deposition of abnormal proteins that can lead to organ dysfunction. It is classified and diagnosed based on the type of protein involved.