The most serious hematological diseases include: acute leukemia, multiple myeloma, malignant lymphoma and so on. 1. Acute leukemia: it is a malignant clonal disease of hematopoietic stem cells. At the onset of the disease, the abnormal primitive and naive cells in bone marrow proliferate in large quantities and infiltrate the liver, spleen, lymph nodes and other organs extensively, inhibiting normal hematopoiesis. Clinically, the onset of the disease varies in urgency, and the acute cases are mostly characterized by high fever or severe bleeding, and the patients often show pale face, fatigue, ecchymosis of mucous membranes and so on. 2. Multiple myeloma: it is a malignant tumor with clonal proliferation of plasma cells in bone marrow. A large number of abnormal plasma cells (or myeloma cells) proliferate monoclonally in the bone marrow, causing osteolytic bone destruction, M protein in the serum, inhibition of normal polyclonal immunoglobulin synthesis, and peripheral proteins in the urine, causing renal function damage, anemia, and immune function abnormality. 3. Malignant lymphoma: originated from lymph nodes and lymphatic tissues, its occurrence is mostly related to the malignant transformation of certain immune cells produced by the proliferation and differentiation of lymphocytes in the process of immune response, and it is a malignant tumor of immune system. Clinically, it is characterized by painless progressive lymph node enlargement and localized lumps, and at the same time, there may be symptoms of corresponding organs being compressed or infiltrated and damaged. If patients suspect the above diseases, they should go to the hospital in time and receive treatment under the guidance of physicians.