Acute lymphoblastic leukemia definition - medical term
An acute (sudden onset), rapidly progressing
form of leukemia that is characterized by the presence in the blood and bone marrow
of large numbers of unusually immature white blood cells destined to become lymphocytes.
Acute lymphoblastic leukemia is also called acute lymphocytic leukemia and is abbreviated
ALL (spoken not as the word "all", but as the three letters A-L-L). ALL is the most
common cancer occurring in children, representing almost 25% of cancer among children.
There is a sharp peak in the incidence of ALL incidence among children ages 2 to
3. This peak is approximately fourfold greater than that for infants and is nearly
10-fold greater than that for youths who are 19 years old.
For unexplained reasons, the incidence of ALL is substantially higher for white
children than for black children, with a nearly threefold higher incidence at 2
to 3 years of age for white children compared to black children. The incidence of
ALL appears to be highest in Hispanic children.
Factors associated with an increased risk of ALL have been identified. The main
environmental factor is radiation, namely prenatal exposure to x-rays or postnatal
exposure to high doses of radiation. Children with Down syndrome (trisomy 21) also
have an increased risk for both ALL and acute myeloid leukemia (AML). About two-thirds
of acute leukemia in children with Down syndrome is ALL. Increased occurrence of
ALL is also associated with certain genetic conditions, including neurofibromatosis,
Shwachman syndrome, Bloom syndrome, and ataxia telangiectasia.
The malignant lymphoblasts from a particular ALL patient carry antigen receptors
unique to that patient. There is evidence to suggest that the specific antigen receptor
may be present at birth in some patients with ALL, suggesting a prenatal origin
for the leukemic clone. Similarly, some patients with ALL characterized by specific
chromosome translocations have been shown to have cells containing the translocation
at the time of birth.
Seventy-five to 80% of children with ALL now survive at least 5 years from diagnosis
with current treatments that incorporate systemic therapy (e.g., combination chemotherapy)
and specific central nervous system (CNS) preventive therapy (i.e., intrathecal
chemotherapy with or without cranial irradiation). Ten-year event-free survival
of multiple large prospective trials conducted in different countries for children
treated primarily in the 1980s is approximately 70%.
Since nearly all children with ALL achieve an initial remission, the major obstacle
to cure is bone marrow and/or extramedullary (e.g., CNS, testicular) relapse. Relapse
from remission can occur during therapy or after completion of treatment. While
the majority of children with recurrent ALL attain a second remission, the likelihood
of cure is generally poor, particularly for those with bone marrow relapse occurring
while on treatment.
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