Definition of Acute Lymphoblastic Leukemia
Acute Lymphoblastic Leukemia (ALL) is a malignant disorder that originates in a single B or T-lymphocyte progenitor. Proliferation and accumulation of blast cells in the marrow result in suppression of hematopoiesis and, thereafter, anemia, thrombocytopenia, and neutropenia. Lymphoblasts can accumulate in various extramedullary sites, especially the meninges, gonads, thymus, liver, spleen, and lymph nodes. The disease is most common in children but can be seen in individuals of any age.
Incidence of Acute Lymphoblastic Leukemia
The age-adjusted incidence rate of Acute Lymphoblastic Leukemia was 1.6 per 100,000 men and women per year in the United States, based on cases diagnosed in 2001 to 2005 from 17 Surveillance, Epidemiology, and End Results (SEER) geographic areas. It is estimated that 5430 cases (3220 males and 2210 females) were diagnosed with Acute Lymphoblastic Leukemia in 2008 in the United States. This number represents approximately 12 percent of all cases of leukemias.
Classification of Acute Lymphoblastic Leukemia
Acute Lymphoblastic Leukemia has many subtypes and can be classified by immunologic, cytogenetic, and molecular genetic methods. These methods can identify biologic subtypes, requiring treatment approaches that differ in their use of specific drugs or drug combinations, dosages of drug, or duration of treatment required to achieve optimal results. For example, cases of childhood Acute Lymphoblastic Leukemia having a hyperdiploid karyotype respond well to extended treatment with methotrexate and mercaptopurine, whereas cases with Philadelphia chromosome and BCR-ABL1 fusion benefit from intensive treatment that includes tyrosine kinase inhibitor and transplantation of allogeneic hematopoietic stem cells in adults.
The relative lack of therapeutic success in adult Acute Lymphoblastic Leukemia is partly related to a high frequency of cases having unfavorable genetic abnormalities and partly related to poor tolerance to intensive treatment. Nearly 90 percent of children and 40 percent of adults can expect long-term, leukemia-free survival—and probable cure—with contemporary treatment. Currently, emphasis is placed not only on improving the cure rate but also on improving quality of life by preventing acute and late treatment-related complications, such as second malignancies, cardiotoxicity, and endocrinopathy.