The different types of cells that make up our blood include white blood cells that fight infection, red blood cells that carry food and oxygen to tissues throughout the body, and platelets that form blood clots and help stop bleeding. The cells that produce each of these different types of blood cells can also become malignant or cancerous, leading to different types of leukemias. Within the broad group of white blood cells, myeloid cells fight bacterial and fungal infections and mediate allergic reactions, and lymphoid cells fight bacteria, virus, and even cancers. When myeloid white blood cells become cancerous, they are called myeloid or myelogenous leukemias. When lymphoid cells become cancerous, we call them lymphocytic leukemias. Another major factor that leads to different types of leukemias is where along the process of blood cell development does the cancer forming process occur. All different types of blood cells begin as very immature or basic blood cells known as blasts. These immature cells then progress along different stages of development until they become highly specialized white blood cells, red blood cells, or platelets. If a cancer hit, or abnormality, develops very early on in the development in a very immature blood cell or blast, this causes acute leukemias. These types of leukemias are associated with very rapid cancer cell growth and patients become quite ill rather quickly. These rapidly growing and dividing acute leukemia cells can be very susceptible to chemotherapy. And this relates to some acute leukemias being curable with aggressive chemotherapy regimens. In contrast, if a malignant or cancerous hit or abnormality develops in a more mature or more developed blood cell, the leukemia cells tend to grow more slowly. These so-called chronic leukemias tend to develop over a longer period of time. And patients are not quite as ill at the time of diagnosis. Though less curable, the chronic leukemias are often quite treatable. Putting this together, we can classify most leukemias under one of four major groups: acute myeloid or acute myelogenous leukemia, chronic myelogenous leukemia, acute lymphocytic leukemia, and chronic lymphocytic leukemia.