Clinical presentations of cell dissemination and metastasis in MM. (A) Skeletal survey showing multiple lytic lesions in the skull of a patient diagnosed with symptomatic multiple myeloma (MM). These multiple lesions represent multiple sites of growth of MM cells within the BM niches in the skull. (B) A PET scan showing multiple areas of enhancement in a patient with extramedullary MM, indicating that MM cells can metastasize to areas outside the BM in a subgroup of patients with extramedullary MM. (C) Extramedullary MM presenting as a large subcutaneous mass on the shoulder of a patient with advanced disease. (D) Circulating tumor plasma cells observed in a patient with MM demonstrating that a small number of tumor cells are continuously circulating in the peripheral blood leading to cell dissemination. This patient does not have plasma cell leukemia.