Acute Leukemias - Republican Scientific Medical Library

a 5.3 · Etiology 87
are inconclusive and may not be specific to ALL [1, 73,
81, 87]. For example, in studies of the health effects of
trichloroethylene, there have been some suggestions of
excess leukemia and other lymphohematopoeitic malignancies
[152], although these data are not compelling,
and leukemia subtypes typically were not reported.
Concerns have also been raised about exposures to petroleum
workers, although recent updates do not implicate
ALL [45, 158].
A few studies have suggested an association between
parental exposures to solvents and childhood ALL. In
one review, direct toxic exposures including solvents,
paints and pigments, and motor vehicle related occupations
were associated with leukemia but not ALL [18]. A
subsequent case-control study reported that mothers of
ALL cases were more likely to report occupational exposure
to solvents (OR = 1.6; 95% CI = 1.1–2.3) and paints or
thinners (OR =1.7; 95% CI = 1.2–2.3) during pregnancy
[135]. A subsequent case-control study in Germany also
found an increased risk of ALL among children whose
mothers were exposed to paints or lacquers but not solvents
or plastics, prior to conception (OR = 1.6; 95%
CI =1.1–2.4) and during pregnancy (OR = 2.0; 95%
CI =1.2–3.3), but not during the postnatal period [132].
Paternal exposures to industrials dusts also showed a
small elevation of risk for ALL. Elevated risks for children
were also found for exposure to artwork solvents
[135] and, in another study, for those living in homes
that had been painted just prior to or during occupancy
[26]. It was noted that solvents, paints, and thinners are
all likely to cross the placental barrier, suggesting a
mechanism of action [135]. However, post pregnancy,
neither maternal exposure to solvents nor parental exposure
to plastic materials was associated with childhood
ALL.
An overriding concern with studies of the risks of
parental exposures is the possibility of recall bias in
the self-reported exposure assessment [18, 89, 133].
5.3.3.2 Pesticides
Numerous studies have examined the association between
lymphohematopoeitic cancers, pesticides and
farming, and they report limited evidence to suggest
an association with ALL. Some recent studies, however,
have suggested a link specifically to childhood leukemia
and ALL. For example, Infante-Rivard and colleagues
found indoor and garden use of pesticides was asso-
ciated with increased rates of childhood ALL, and some
of these associations were increased among carriers of
the CYP1A1m1 and CYP1A1m2 mutations [48].
In the Northern California Childhood Leukemia
Study, the use of professional pest control services any
time from 1 year before to 3 years after birth was associated
with a significantly increased risk of childhood
leukemia (OR = 2.8; 95% CI=1.4–5.7), with the highest
risk associated with exposure during the second year
(OR = 3.6; 95% CI = 1.6–8.3). Children with the most frequent
exposure to insecticides had the highest risk of
leukemia (OR = 2.4; 95% CI=1.2–5.1), and leukemia risk
was elevated for exposure to indoor insecticides
(OR = 1.6; 95% CI = 1.0–2.7); exposures to outdoor insecticides
or herbicides were not associated with leukemia
risk [83]. A subsequent California case control study
found small but statistically significant elevations of
ALL risk for maternal residential proximity to areas
of use of certain agricultural pesticides [115]. Most recently,
Menegaux and colleagues reported that childhood
ALL was statistically significantly associated with
maternal indoor use of pesticides during pregnancy and
childhood and garden use of pesticides during childhood
[90].
5.3.3.3 Outdoor Air Pollution
Some researchers have suggested that outdoor air pollution
may be a risk factor for leukemia. Various hypotheses
exist, most notably that the risk is attributable
to benzene, a component of automobile exhaust. To investigate
this, investigators have conducted more than a
dozen studies in the USA and Europe, assessing the possible
association between leukemia incidence or mortality
and various measures of traffic density, a crude surrogate
for air pollution [19, 23, 61, 68, 101, 103, 110, 113,
114, 129, 142, 150]. Some specifically analyzed ALL risk.
Of these studies, eight reported a positive association
for childhood leukemia; five did not. It is difficult to
draw a conclusion as studies varied by design, exposure
measure and adjustments for confounding.
A California study using modeled concentrations of
25 potentially carcinogenic hazardous air pollutants
(HAPs) provided by the US Environmental Protection
Agency at the census tract level, reported an association
of HAPs with childhood leukemia [116]. Their analysis
showed elevated rate ratios and a statistically significant
trend in the tracts ranked highest for the combined 25