1. Hematopoietic system and blood production To understand leukemia, we must first understand the hematopoietic system and the hematopoietic process. The human body is composed of several systems, organs and tissues, performing their different physiological functions, which organ function abnormal, the body will get the corresponding disease. Among them, the hematopoietic system performs hematopoietic and immune functions. The hematopoietic system is composed of hematopoietic tissues and blood cells. Hematopoietic tissues include bone marrow, liver, spleen, lymph nodes, etc. Bone marrow is the main hematopoietic tissue. Blood cells are the main component of blood and include three major types, namely white blood cells, platelets and red blood cells. These blood cells are mainly produced in the bone marrow. The process of production in the bone marrow is briefly summarized as follows: hematopoietic stem cells differentiate into progenitor cells of various lineages, further differentiate into primitive stage cells of various lineages, continue to differentiate into cells of their respective naive stages, and finally differentiate into mature stage blood cells, which are released from the bone marrow into the blood and tissues to perform their functions. 2. What is leukemia Leukemia is commonly known as “blood cancer”, a common malignant tumor of the hematopoietic system, which occurs in the bone marrow. It is characterized by the abnormal proliferation of a series of primitive and naive blood cells (leukemia cells) in the bone marrow, which are released into the bloodstream and can involve hematopoietic organs such as liver, spleen, lymph nodes and other non-hematopoietic organs. Due to the large number of leukemic cells growing in the bone marrow, its normal hematopoietic function is inhibited, resulting in a decrease in the production of normal blood cells, which causes the three main clinical manifestations of anemia, infection and bleeding. As leukemia cells invade various tissues it may cause enlargement of liver and spleen, lymph nodes, bone pain and other organs with corresponding manifestations.