The incidence rate of childhood ALL varies internationally (≈4-40/106 per year) (Greaves, 1999). It occurs at a higher rate in males than females. Leukemia is one of the top 15 most frequently occurring cancers in minority groups. Leukemia incidence is highest among whites and lowest among American Indians/Alaskan natives. Leukemia rates are substantially higher for white children than for black children. Hispanic children of all races under the age of 20 have the highest rates of leukemia. CLL and AML incidence increase dramatically among people who are over the age of 50, and CML incidence increases dramatically among people who are over the age of 60. These cancers are most prevalent in the seventh, eighth and ninth decades of life.
Childhood ALL is the most common pediatric cancer in developed countries. Common ALL is the most prevalent and accounts for 60%-70% of all ALL cases, with a peak incidence between ages 2 and 5. T-ALL accounts for 10%-25% of ALL in the Western World, with a male dominance, older age at onset, and a constant incidence rate during childhood (Toren, et al., 1996). The incidence of ALL among 1- to 4-year-old children is more than 10 times greater than the rate for young adults ages 20-24.
The apparent increased risk (~10 times) for cALL in ‘developed’ countries probably arises as a consequence of a rare, pathological response to delayed exposure to one or more types of microorganisms that, in less developed communities, are transmitted neonatally or in infancy. Family size, crowding, hygiene, and associated ‘herd immunity’ status would be the critical determinants. cALL would then be the outcome of a rare response to a common infection. ALL might be a response to a common virus (Greaves, 1999).
The peak age for childhood leukemia is 2-5 years old. A study done by the United Kingdom childhood cancer study examined the effects of social activity and the rate of occurrence for different types of leukemia. They found that as social activity increased, the risk of getting leukemia decreased. The greatest reduction in the risk of ALL was seen in children who attended formal day care during the first three months of life (Gilham, et al., 2005). Children attending day care centers on a regular basis in the first few months of life are less likely to develop acute lymphoblastic leukemia than children who do not. This is thought to be likely because of the increased exposure to common infections.
The usual ALL peak at the age of 2 to 5 is absent in Africa and other developing countries; T-ALL and B cell lymphoma are more prevalent (Toren, et al., 1996). Both T-ALL and cALL have a lower apparent incidence rate in children of black or mixed ethnic origin compared with white Caucasian groups but the deficit is much more pronounced for cALL.
Hyperdiploid (≥52 chromosomes) childhood leukemias, especially those with a high hyperdiploid modal number, seem to be more frequent and ALL-specific translocations less frequent in the Nordic countries than in other geographic regions. Systematic differences in exposure to environmental oncogenic factors or in geographic/ethnic origin are a possibility for this difference.
Caribbean and Japanese Islands
The two endemic areas for leukemia are the black population in the Caribbean Sea islands and the islands south of Japan (Raileanu, 1993). Caribbean T-cell lymphoma/leukemia (CATL): CATL occurs in black patients born in the Caribbean. CATL predominantly affects females and occurs in patients with a median age of 45 years. CATL is very similar to Japanese adult T-cell lymphoma/leukemia (JATL). Female predominance does not occur in JATL, nor any other reported T-cell lymphomas. JTAL is most frequently seen in patients born in rural and costal areas of southwestern Japan. (Swerdlow, et al., 1984).
Created by Shannon McGlauflin, Jolene Munger, and Rebecca Nelson, 2005.