Leukemia is a cancerous disease caused by abnormal activity of stem cells (immature cells that originate in the bone marrow). There are two main types of leukemia - myelogenous and lymphocytic (according to the type of cells involved), which can be further classified in two categories - acute and chronic.

Acute leukemia is characterized by the rapid multiplication of partially developed, functionless cells. These abnormal cells accumulate inside the bone marrow or in the blood stream, interfering with the activity of normal, healthy cells. People with acute leukemia also suffer from anemia, which is caused by a pronounced decrease in the number of red blood cells. Leukemia sufferers also have a deficit of healthy white cells, which have a vital role in fighting against infections. In addition, acute leukemia affects the body's production of platelets, which have an important role in blood coagulation (they speed up the healing of open wounds).

Chronic leukemia also causes serious impairments at cellular level, triggering an overproduction of abnormal cells. However, unlike acute leukemia, chronic forms of the disease allow the affected cells to reach more advanced stages of development. Thus, chronic leukemia has a slower rate of progression.

The annual prevalence of leukemia among the population of the United States is around 31.000 new cases. Leukemia has the highest incidence in older adults, commonly affecting people with ages over 60. However, there are certain types of leukemia that predominantly affect children. For instance, acute lymphocytic leukemia (ALL) is responsible for causing more than 80 percent of overall childhood leukemia cases.

In adults, the most common types of leukemia are acute myelogenous leukemia (AML) and chronic lymphocytic leukemia (CLL). Acute myelogenous leukemia accounts for more than 10.000 new cases each year, while chronic lymphocytic leukemia is responsible for causing around 8.000 new annual cases.

Leukemia has the highest incidence in the male gender. Statistics indicate that more than 56 percent of annual leukemia cases are diagnosed in men. Although it can be seen in all ethnical groups, leukemia predominantly affects Caucasian white people. The annual incidence of leukemia is lower in African Americans, while American Indians and Hispanics rarely develop the disease. Similarly, leukemia is rarely seen in Asian people.

The most common type of leukemia among children aged 3-15 is acute lymphocytic leukemia. Due to the fact that acute lymphocytic leukemia predominantly affects children, it is referred to as childhood leukemia. Childhood leukemia rarely affects children younger than 3 or with ages over 15. Despite the fact that modern medicine doesn't hold the cure for childhood leukemia, the medical treatments and therapies available nowadays can slow down the progression of the disease and in some cases, they can even overcome leukemia completely. The annual morbidity rate of leukemia among young patients has known a considerable decrease in the last two decades. Thanks to modern medical equipment, leukemia can be timely diagnosed, allowing prompt medical intervention. Nowadays, early diagnosis and new approaches in medical treatment can considerably extend patients' life-expectancy, thus increasing the chances of complete recovery.