Acute Leukemias - Republican Scientific Medical Library

78 Chapter 5 · Acute Lymphoblastic Leukemia: Epidemiology and Etiology
In this review, we present first the descriptive epidemiology
of ALL (Table 5.1), mainly using incidence and
survival data from the US National Cancer Institute’s
Surveillance, Epidemiology and End Results (SEER)
Program (http://seer.cancer.gov), and mortality data
from the US National Center for Health Statistics
(http://www.cdc.gov/nchs/deaths.htm), followed by a
brief discussion of parental and sociodemographic
characteristics of ALL cases. Where possible, in our discussion
of the descriptive epidemiology, we report patterns
for race and gender specific subgroups. However,
when looking at trends or individual years, subgroup
data often are not reported due to small numbers of
events.
We then review the published literature on biological,
physical, and chemical risk factors for ALL. Because
the incidence of ALL peaks around the third birthday,
our discussion of the etiology of ALL will focus more
on the pediatric population. Our review is neither exhaustive
nor comprehensive, but rather summarizes
our view of key findings in understanding the patterns
and etiology of this disease.
5.2 Demographic Patterns
5.2.1 Incidence
ALL represents approximately less than 1% of adult cancers,
and 25% of all childhood cancers. In the USA,
among all ages, it represents less than 0.4% of all cancers,
13.6% of all leukemias, and 29.6% of all lymphocytic
leukemias. Age-adjusted incidence rates for ALL vary
several-fold, internationally, with the highest rates occurring
in Spain, among Hispanics in Los Angeles,
and in Caucasians in Quebec and Ontario, Canada,
and in New Zealand. The lowest rates are found in developing
countries, among US blacks, Israeli Jews, and
Chinese and Asian Indians, whose rates may be many
times lower than those in more affluent, developed
countries [42, 75].
Among children under age 20, ALL is the most common
malignancy, except in Africa and the Middle East.
The highest rates of childhood ALL occur in Costa Rica
and among Hispanics in Los Angeles, and the lowest
rates among US blacks, in the Middle East, and in India
[38, 75]. In the US, it represents almost 25% of all childhood
cancers and 79.5% of all childhood leukemias, and
99% of all lymphocytic leukemias (Table 5.1). Despite
being the most common type of cancer in children, it
remains a relatively rare disease in both children and
the total population (3.6 and 1.4 cases per 100 000 per
year, respectively).
When we compare the secular trends of ALL to
those of all leukemias, we see some marked differences.
Secular trends in leukemia for the entire US population
show that incidence rates from 1975 to 2001 decreased
slightly for white males and increased slightly for white
females (–0.1%, 0.2% per year, respectively), but from
2001 to 2003 rates for white females decreased rapidly
(–6% per year). For black males and females from
1975 to 2003 the rates for leukemia decreased (–0.7%,
–0.6% per year, respectively). In males, for whites and
blacks combined, ALL incidence rates increased from
1975 to about 1990, and then declined through 2002,
while female ALL incidence rates showed a very slight
increase until the late 1990s, when they also began to decline.
In children of both genders and races, total leukemia
incidence rates increased at a rate of about 1.0% per year
from 1975 to the late 1980s, apparently driven by ALL,
which increased at about 1.8% per year during this same
period [117]. Some have suggested that this greater increase
in ALL is due to improved characterization of
leukemia subtypes, information that was obtained to
help physicians specify appropriate treatment agents
[77, 117]. From the late 1980s on, incidence rates both
for total leukemia and for ALL increased at a rate of
about 0.3% per year [117].
5.2.2 Survival
Less than half of all adult leukemias survive 5 years after
diagnosis, but nearly two-thirds of all adult ALL cases
survive at least 5 years after diagnosis. Childhood leukemia
survival is much better than that for adults, with
more than three-quarters of all children with leukemias
and more than four-fifths of ALL cases surviving at least
5 years past diagnosis [117]. Childhood ALL survival is
one of the most dramatic success stories in the history
of chemotherapy, showing a remarkable improvement
due to innovative treatments, with the 5-year survival
rate in 1964 being only 3% [162], rising to 57% in
1975–1977 and 87% in 1996–2002 (Fig. 5.1) [117].