Leukemia: Types

In the same way that family trees may be divided into blood lines, the five types of leukocytes (white blood cells) are divided into two groups (lineages), based on their developmental pathways. The myeloid cells includes monocytes, neutrophils, eosinophils and basophils. The lymphoid cells includes B lymphocytes, T lymphocytes, and Natural Killer (NK) cells. Learn more about lymphocytes

Leukemias are classified into 4 main categories, based on the type of white blood cell affected (lymphoid vs. myeloid) and characteristics of the disease (acute vs. chronic):

• Acute Lymphoblastic Leukemia
• Acute Myeloid Leukemia (Acute Myelogenous Leukemia)
• Chronic Lymphoid Leukemia (Chronic Lymphocytic Leukemia)
• Chronic Myeloid Leukemia (Chronic Myelogenous Leukemia)

Acute leukemias are generally aggressive diseases in which cancerous transformation occurs at early stages in the development of the affected blood cell. If untreated, these diseases can be rapidly fatal.⁽¹⁾
Chronic leukemias are characterized by a slower progression than acute leukemias. These leukemias are more difficult to cure, so the approach to therapy is often conservative and aimed at controlling symptoms.⁽²⁾

Acute Leukemia
Acute leukemias are caused by damage to stem cells or cells in the early stages of development in the bone marrow. Mutations affecting control of cell division, differentiation, and cell death lead to the accumulation of early blood cell precursors known as blast cells.⁽¹⁾

Acute Lymphoblastic Leukemia (ALL)
ALL is the most common form of leukemia diagnosed in children.⁽³⁾ The incidence of ALL peaks between the ages of 3-7, falls by 10 years of age, and rises again after the age of 40.⁽⁴⁾

Acute Myeloid Leukemia (AML)
AML represents 10-15% of leukemias diagnosed in childhood and is the most common type of acute leukemia diagnosed in adults.⁽⁵⁾

Chronic lymphoid leukemias are diseases characterized by the accumulation of fully developed B or T lymphocytes in the blood. These diseases are closely related to lymphomas, in which lymphocytes accumulate in lymph nodes and vessels.⁽⁶⁾

Chronic Lymphocytic Leukemia (CLL)
By far the most common type of chronic lymphoid leukemia, involves B lymphocytes. CLL mainly affects elderly individuals, with a peak incidence between 60 and 80 years of age. ⁽⁶⁾ It is the most common form of leukemia in Western countries.⁽⁷⁾ CLL follows a variable course, with survival ranging from months to decades.⁽⁷⁾

Other types of chronic lymphoid leukemias include:⁽⁶⁾

• Prolymphocytic leukemia (PLL)
• Hairy cell leukemia (HCL)
• Plasma cell leukemia
• Large granular lymphocytic leukemia
• T-cell prolymphocytic leukemia (T-PLL)

Chronic Myeloid Leukemia (CML)
CML is a disorder of a hematopoietic stem cell. The disease, which accounts for approximately 15% of leukemias, occurs most frequently between the ages of 40 and 60 years. Laboratory tests reveal increased numbers of cells belonging to the myeloid cell line (monocytes, neutrophils, basophils, eosinophils) at various stages of development circulating in the blood stream.⁽²⁾

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