Lymphoid leukemia

Lymphoid leukemia or lymphocytic leukemia is a type of leukemia affecting circulating lymphocyte cells. This is in contrast to lymphoma, which is a solid tumor of the same type of cells.

Lymphocytes are a subtype of white blood cells. Most lymphoid leukemias involve a particular subtype of lymphocytes, the B cell.

Classification
Historically, they have been most commonly divided by the stage of maturation at which the clonal (neoplastic) lymphoid population stopped maturing:
 * Acute lymphoblastic leukemia
 * Chronic lymphocytic leukemia

However, the influential WHO Classification (published in 2001) emphasized a greater emphasis on cell lineage. To this end, lymphoid leukemias can also be divided by the type of cells affected:
 * B-cell leukemia
 * T-cell leukemia
 * NK-cell leukemia

The most common type of lymphoid leukemia is B-cell chronic lymphocytic leukemia.

B-cell leukemias
B-cell leukemia describes several different types of lymphoid leukemia which affect B cells.

Other types include (with ICD-O code):
 * 9826/3 - Acute lymphoblastic leukemia, mature B-cell type
 * 9833/3 - B-cell prolymphocytic leukemia
 * 9940/3 - Hairy cell leukemia

T-cell leukemias
T-cell leukemia describes several different types of lymphoid leukemias which affect T cells.

The most common T-cell leukemia is precursor T-cell lymphoblastic leukemia. It causes 15% of acute leukemias in childhood, and also 40% of lymphomas in childhood. It is most common in adolescent males. Its morphology is identical to that of precursor B-cell lymphoblastic leukemia. Cell markers include TdT, CD2, CD7. It often presents as a mediastinal mass because of involvement of the thymus. It is highly associated with NOTCH1 mutations.

Other types include:
 * Large granular lymphocytic leukemia
 * Adult T-cell leukemia/lymphoma
 * T-cell prolymphocytic leukemia

In practice, it can be hard to distinguish T-cell leukemia from T-cell lymphoma, and they are often grouped together.