There are some blood disorders that are really not leukemia at the time of diagnosis, but during the evolution of the disease some patients will transform into leukemia, which is generally called secondary leukemia. The following diseases have the potential to transform into leukemia: 1. Myelodysplastic syndrome (MDS): MDS is a group of clonal hematopoietic disorders that manifest as pathological hematopoiesis in the bone marrow and a decrease in peripheral blood cells, which are classified in the 2008 WHO classification as refractory unilineage hematocrit, refractory multilineage hematocrit, refractory anemia with cyclic iron granulocytosis, primitive refractory anemia with cytosis, MDS in the presence of independent 5q-, MDS that cannot be classified, and childhood MDS. These diseases are not leukemias, but some patients will gradually evolve into acute myeloid leukemia after several months or years. 2. Primary thrombocythemia (ET): Due to genetic abnormalities, the bone marrow has an excess capacity to produce platelets, which is manifested by an excessive proliferation of platelet-producing megakaryocytes in the bone marrow and a significant increase in peripheral blood platelets, and patients are at a dramatically increased risk of thrombosis. It has been reported that 0.6-5% of ET patients will transform into acute myeloid leukemia. 3. True erythrocytosis (PV): Due to genetic abnormalities, the bone marrow has an excess capacity to produce red blood cells, which is manifested by excessive proliferation of red lineage cells in the bone marrow and a marked increase in peripheral blood red blood cells and hemoglobin concentration. A small number of patients will also gradually evolve and progress to acute myeloid leukemia during the course of the disease, with reported rates ranging from 1.5% to 13.5%. 4.Primary myelofibrosis (PMF): fibrosis of bone marrow occurs, with loss of hematopoietic function and replacement of hematopoiesis by extramedullary organs such as the spleen and liver, and a small number of patients also progress to leukemia. 5. Paroxysmal sleep hemoglobinuria (PNH): a hemolytic anemia caused by genetic abnormalities of acquired hematopoietic stem cells, which may manifest as a decrease in whole blood cells. A small number of patients also progress to leukemia. 6. Lymphoma: A small number of inert B-cell lymphomas will undergo transformation to aggressive lymphoma, which will show characteristics of lymphocytic leukemia when the bone marrow is involved. Summary: The common feature of these diseases is the occurrence of genetic abnormalities in hematopoiesis, resulting in a variety of different pathological processes and clinical manifestations, and in some cases other chromosomal and genetic abnormalities will continue to occur during the evolution of disease progression, eventually appearing as leukemia, in fact, there are some differences between this leukemia and primary leukemia in the pathological process, more difficult to treat and worse prognosis.