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INTRODUCTION

In acute lymphoblastic leukemia (ALL), the malignant clone arises from hematopoietic progenitors in the bone marrow or lymphatic system resulting in an increase of immature nonfunctioning leukemic cells. Infiltration of bone marrow leads to anemia, granulocytopenia, and thrombocytopenia with the clinical manifestations of fatigue, weakness, infection, and hemorrhages. These symptoms are more often the reason a patient first seeks medical advice rather than consequences of tumor bulk, such as lymph node enlargement, hepatosplenomegaly caused by leukemic infiltration, or symptoms of the central nervous system (meningeosis leukemica).

The diagnosis of ALL is made by morphology from smears of peripheral blood or bone marrow. The classification includes cytochemistry, immunological markers, cytogenetic, and molecular genetic analysis.

INCIDENCE AND AGE

ALL is the most frequent neoplastic disease in children with an early peak at the age of 3–4 years. The incidence in adults ranges from 0.7 to 1.8/100,000 per year, being somewhat higher in younger adults (1–1.5 for the age group 15–24 years) and decreasing thereafter, only to increase again in elderly people to 2.3 for age >65 years. The frequency of immunological, cytogenetic, and genetic subtypes changes with age.

ETIOLOGY

The etiology of acute leukemias is unknown. There are, however, internal and external factors that influence the incidence of leukemia. In ALL, inheritance of certain diseases and exposure to ionizing radiation or to chemicals, including prior chemotherapy, are associated with an increased risk of developing leukemia, but less than in acute myeloid leukemia (AML).

CONGENITAL DISORDERS

Patients with some rare congenital chromosomal abnormalities have a higher risk of development of acute leukemia; e.g., Klinefelter’s syndrome, Fanconi’s anemia, Bloom’s syndrome, ataxia telangiectasia, and neurofibromatosis. There is a twentyfold increased incidence of leukemia in patients with Down syndrome, in whom ALL is increased in childhood or AML at an older age. Genetic predisposition may play a part in acute leukemia even, when not associated with another inherited disease, as the identical twin of a leukemic child has a fivefold risk of developing acute leukemia.

INFECTIOUS AGENTS

Human T-cell leukemia virus I (HTLV-I), endemic in Japan and the Caribbean, is the etiological agent for adult T-cell leukemia/lymphoma, an aggressive adult T-cell leukemia (see Chap. 196). In the endemic African type of Burkitt’s lymphoma, the Epstein-Barr virus, a DNA virus of the herpes family, has been implicated as a potential causative agent.

DIAGNOSIS AND CLASSIFICATION

The diagnosis of acute leukemia is made by examination of the peripheral blood and bone marrow. Classification of the patient’s disease also requires cytochemical stains, assessment of expression of immunological markers, cytogenetic analysis, and molecular markers. The major aim of classification is to distinguish between AML and ALL because of the different treatment approaches and drug sensitivities. The immunological markers are the major criteria ...

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