ALL is characterized by proliferation and accumulation of malignant, degenerated, immature hematopoietic cells, called blasts, in bone marrow and blood. It is the most common malignant tumor disease of childhood with an incidence peak of 2-5 years. Although ALL is primarily a disease of the bone marrow and blood, all other lymphoid (e.g., lymph nodes, spleen) and non-lymphoid organs (e.g., liver, CNS, skin, bone) may also be affected.
The leukemic blasts displace the physiological leukopoiesis, erythropoiesis, and thrombopoiesis and cytopenias of all three cell lines occur. This is followed by susceptibility to infection, anemia and coagulation disorders. Furthermore, flu-like symptoms, enlarged lymph nodes, hepatosplenomegaly and bone pain are common.
The pathogenetic causes of ALL remain unclear in most cases. It is known that children with certain inherited or acquired immunodeficiencies or with certain chromosomal changes (for example, trisomy 21) have a significantly increased risk of developing ALL. But other factors can also promote the development of leukemia. These include radioactive rays and x-rays, medicines, viruses and contact with certain chemical substances.
Depending on the progenitor cell, immunophenotyping can differentiate between two main groups of ALL: T cell ALL (25% of cases) and B cell ALL (75% of cases). Leukemias can be leukemic (leukocytes elevated), subleukemic (leucocytes normal or depressed), or aleukemic (blasts in the bone marrow but not detectable in the blood). Characteristic is the absence of medium-sized leukocytes (hiatus leucaemicus). Therapeutically, chemotherapeutic drugs and/or allogenic stem cell therapies are available. On average, 35-50% of ALL patients can be cured. The prognosis, however, is not unambiguous with this probability, since it has a wide fluctuation range, depending on the risk group.