Leukemia is a disorder of the bone marrow that affects the white blood cells and the lymphatic system. The body’s white blood cells are responsible for fighting infections. They divide and grow in a systematic manner as per the requirements of the body. When a person develops leukemia, the bone marrow starts producing an excess quantity of abnormal white blood cells, which do not perform their regular functions. These abnormal white blood cells crowd the bone marrow and affect the production of healthy red blood cells and platelets in the blood. In this way, leukemia impairs the functions of these cells.

Leukemia can either be acute or chronic Here is some additional information about them:

• Acute leukemia occurs when the abnormal white blood cells produced in the bone marrow do not grow, and so, do not perform their usual functions. This condition occurs suddenly, and the cancerous cells multiply and grow rapidly. These cells may spread to other organs in the body as well. It is the most common form of leukemia that affects children and needs to be treated immediately.
• Chronic leukemia occurs gradually, where abnormal cells grow and mature fully. The symptoms appear after the onset. In the initial stages, the symptoms may be mild, and the disease takes months or years to progress. Chronic leukemia is seen mostly in older people but can affect people of any age. This condition can be monitored, and treatment can be undertaken in a timely way.

There are different types of white blood cells in the body like lymphocytes and myeloid cells. Leukemia affecting the lymphocytes is called lymphocytic or lymphoblastic leukemia, and leukemia that affects the myeloid cells is called myelogenous leukemia. Based on this, leukemia is further categorized into specific types.

• Acute lymphocytic leukemia (ALL): Acute lymphocytic leukemia is common in young children, although it can occur in adults too.
• Chronic lymphocytic leukemia (CLL): CLL is the most common form of chronic leukemia that affects adults. As it is chronic in nature, the symptoms may not appear for years.
• Acute myelogenous leukemia (AML): Acute myelogenous leukemia is quite common and can occur in both children and adults. It most commonly affects adults.
• Chronic myelogenous leukemia (CML): Symptoms do not appear for months or years, but after they do, the rapid growth phase starts. CML mostly affects adults.

There are some rare types of leukemia which resemble the more common types but cannot be grouped with them.

• Large granular lymphocytic leukemia: This form of leukemia is not aggressive.
• T-cell prolymphocytic leukemia: It is an aggressive form of leukemia that affects adults, but is quite rare. This is the most common type of leukemia that affects T-cells.
• Adult T-cell leukemia: This type is caused by a virus similar to HIV, called human T-lymphotropic virus (HTLV). This virus is confined to (endemic to) certain parts of the world.
• Hairy cell leukemia (HCL): HCL is similar to ALL, but cannot be categorized as such. This type has not been reported in children, and 80% of the cases were male adults. HCL is treatable but has no cure.
• Clonal eosinophilias: This form of leukemia affects the eosinophils, a type of white blood cell.

Pre-leukemia occurs when a clone of a non-cancerous blood cell multiplies rapidly. One type of pre-leukemia only affects people with Down’s syndrome (a genetic disorder) or other genetic changes. Transient myeloid leukemia is another form of pre-leukemia.