Plasma cell leukemia and multiple myeloma are two different stages of the same disease. Multiple myeloma is diagnosed when there are ≥10% myeloma cells in the bone marrow, and when there is bone pain, renal impairment, elevated blood calcium, and bone destruction. When the proportion of plasma cells in peripheral blood leukocytes is ≥5% in patients with multiple myeloma, plasma cell leukemia can be diagnosed. Therefore, plasma cell leukemia is a condition in which the plasma cells in peripheral blood are significantly elevated in patients with multiple myeloma, that is, ≥5% is a further development of multiple myeloma, and the prognosis is worse than that of multiple myeloma, which is a relatively The prognosis is worse than that of multiple myeloma, which is a relatively inert hematologic malignancy, but plasma cell leukemia has a poor prognosis.