Leukemia

Blood cells are produced in the bone marrow before either maturing there or traveling to the thymus to mature.

Leukemia arises when a blood-cell precursor in the bone marrow acquires mutations that drive uncontrolled proliferation. The abnormal cells accumulate and crowd out normal hematopoiesis, leading to failure of red cells, normal white cells, and platelets. It is broadly divided into acute and chronic forms, and further by the cell line involved (myeloid or lymphoid).

Acute Leukemia:

Acute leukemia is driven by rapidly proliferating immature cells, so bone marrow failure develops quickly and treatment must be aggressive and started early. Lymphoblastic disease is the main type seen in children. Without treatment the acute forms progress over a matter of weeks, making prompt diagnosis critical.

Chronic Leukemia:

In chronic leukemia the affected cells proliferate slowly, so the disease is less immediately aggressive and may be managed with less intensive treatment. It can take years to become life-threatening but requires monitoring, as it can transform into an acute leukemia.

Myeloid Leukemia

Myeloid leukemias affect the granulocyte and monocyte cell lines. On a blood film, myeloperoxidase can be demonstrated by cytochemical staining, helping to identify the myeloid origin. Chronic myeloid leukemia (CML) is strongly associated with a characteristic chromosomal abnormality and tends to progress slowly, with falling hemoglobin and hepatomegaly appearing as the marrow becomes suppressed. Acute myeloid leukemia (AML) presents with failure of all three blood cell lines — anemia, low platelets, and a white cell count that may be very high early on but falls in later stages.

Lymphoblastic Leukemia

Lymphoid leukemias affect T-cells, B-cells, and NK cells. Positive nuclear staining for TdT (a DNA polymerase found only in lymphoblasts) identifies the lymphoid origin, with surface markers used to distinguish T-cell from B-cell disease. Chronic lymphocytic leukemia (CLL) is the most common form of leukemia, mainly affecting older men; it predominantly involves B-cells, causing immunocompromize, and progresses so slowly that many patients die of other causes first. Acute lymphoblastic leukemia (ALL) again presents with low red cells, platelets, and abnormal white cell counts as the marrow is overtaken.

Symptoms reflect the loss of normal blood cells and the infiltration of tissues by leukemic cells. Common features include fatigue and pallor from anemia, recurrent or persistent infections from a lack of functional white cells, and easy bruising or bleeding from low platelets. Bone pain, fever, night sweats, weight loss, swollen lymph nodes, and an enlarged liver or spleen are also frequently seen.