Leukemia

Leukemia is a group of cancers that start in the blood-forming cells of the bone marrow. A developing blood cell acquires genetic changes that let it multiply out of control, and its abnormal descendants, usually white blood cells or their precursors, pack the marrow and spill into the blood. Crowding out normal blood production, they cause anemia, with tiredness and pallor; a shortage of platelets, with easy bruising and bleeding; and a shortage of working white cells, with repeated infections. Leukemic cells can also invade the lymph nodes, spleen, liver and nervous system.

Leukemias are classified by the cell line involved, lymphoid or myeloid, and by pace. Acute leukemias consist of very immature cells called blasts and worsen within weeks if untreated; chronic leukemias involve more mature cells and progress slowly. This gives four main types: acute lymphoblastic leukemia (ALL), the most common childhood cancer; acute myeloid leukemia (AML), mostly in older adults; chronic lymphocytic leukemia (CLL), common in older adults in Western countries; and chronic myeloid leukemia (CML), driven by the BCR-ABL fusion gene on the Philadelphia chromosome.

Diagnosis relies on a blood count and smear, a bone marrow biopsy, flow cytometry and genetic tests. Treatment may include chemotherapy, targeted drugs such as tyrosine kinase inhibitors for CML, immunotherapy including CAR T cells, and stem cell transplantation.