Pediatr Blood Cancer 2007;49:607608
HIGHLIGHTby Julie A. Ross, PhD1,2*
Looking for Leukemia Clues in of all Places. . . :Meconium!(Commentary on LaFiura et al., pp. 624628)
B ecause of the rarity of childhood cancer, epidemiologistsnecessarily rely on the case-control approach. In thesestudies, parents of cases and of healthy children are typically
interviewed via questionnaire regarding exposures and experiences
prior to the development of cancer in the case child and some
predetermined date in the control child. It is difficult to interpret
these studies, since we are relying on sometimes faulty recall.
Moreover, potential hot-button questionnaire items can trigger
additional angst and perhaps additional recall among case
parents. For example, for pesticides, a case mom might recall a
one-time episode in the first trimester of pregnancy when a
pesticide was used in the kitchen to spray for ants where a
control mom might not report such an event since she would not
believe it to be noteworthy. Importantly, several epidemiologic
studies have shown positive associations between pesticide
exposure and certain childhood cancers [1,2], thus one of our major
challenges is to devise ways to improve exposure and/or validate
study results using other disciplines. Animal studies can provide
certain clues, since exposure to high levels of certain pesticides can
be experimentally carcinogenic. Another avenue is the creative use
of biological specimens available at birth.
For example, studies of chromosomal rearrangements present at
birth are helping to inform the natural history of childhood
leukemia. Many chromosomal rearrangements occur in childhood
acute lymphoblastic leukemia (ALL) and acute myeloid leukemia
(AML), but a few predominate. About 80% of ALL and 60%
of AML among infants diagnosed less than 1 year of age show
rearrangements of the MLL gene at chromosome band 11q23 and
one of several partner chromosomes including most commonly,
chromosomes 4, 9, or 19 [3,4]. Among children aged 115 years,
rearrangements involving theETV6 gene on chromosome12 and the
RUNX1 gene on chromosome 21 (known as TEL-AML1) are found
in approximately 25% of childhood ALL . RUNX1 is also
involved in AML, with chromosomal translocations with a gene,
ETO, on chromosome8 present in about 15%of cases.Of note, these
samegene rearrangements (MLL-various partner genes,TEL-AML1
and AML1-ETO) have been identified in neonatal blood spots
collected at birth [6,7]. Twins with leukemia also share the same
non-constitutive rearrangements . These molecular observa-
tions provide strong evidence that many childhood acute leukemias
are initiated in utero. However, with the exception of MLL gene
rearrangements, where it is still unclear what additional mutation(s)
may be needed [11,12], TEL-AML1 and AML1-ETO are insufficient
for frank leukemia development. About 1 in 100 cord blood samples
from healthy children have the TEL-AML1 gene rearrangement, and
about 1 in 500 have the AML1-ETO rearrangement . These
observations provide strong evidence that additionalmutationsmust
occur before leukemia develops in most children.
In this issue, Ge Yet al.  report on an elegant pilot study that
examines correlations between specific pesticides present in
meconium (i.e., an infants first bowel movement) and the AML1-
ETO translocation in cord blood samples of healthy children.
Meconium is an appropriate sample for these types of studies since it
can provide a cumulative picture of pesticide exposure throughout
the pregnancy. The investigators used a population of newborn
infants from the Philippines where agricultural and home pesticide
use is common. From a total of 49 infants,meconium analysis by gas
chromatography/mass spectrometry revealed that 39 infants were
exposed to the pesticide, proxopur, sometime during the in
utero period, while 10 were unexposed. Total RNAs were also
isolated from the 49 cord blood samples and nested RT-PCR
was used to identify AML1-ETO fusion transcripts; if positive,
the fusion transcript form was also identified. A total of 8/39
proxopur-exposed infants and 1/10 proxopur-unexposed infants had
theAML1-ETO transcript present in cord blood. Intriguingly, for the
exposed infants, the AML1-ETO transcript levels were positively
correlated with proxopur concentrations in the meconium. Further,
the one infantwith the highest level ofAML1-ETO fusion transcripts
was exposed to two pesticides, proxopur and cypermethrin. Of note,
the level of AML1-ETO transcript in this infants cord blood was
only about eightfold lower than levels reported from diagnostic
AML blast samples. Fortuitously, the investigators were able to
examine a peripheral blood sample from this infant 1 year later and
found that the AML1-ETO transcripts were 300-fold lower than the
childs cord blood sample. These results reinforce the necessity
for additional genetic mutations (and perhaps environmental
exposure(s)) prior to the development of overt leukemia in children
with these translocations at birth.
This study is important on many fronts. While it is recognized
that it is a pilot, it shows how useful a maternalfetal cohort study
can be in helping to inform childhood cancer epidemiology studies.
Because of the rarity of childhood cancer overall, however, it will be
2007 Wiley-Liss, Inc.DOI 10.1002/pbc.21308
Division of Epidemiology & Clinical Research, University of
Minnesota, Minneapolis, Minnesota; 2Division of Population
Sciences, University of Minnesota Cancer Center, Minneapolis,
Julie A. Ross is Professor and Director of the Division of
Epidemiology & Clinical Research and also Associate Director for
Population Sciences in the University of Minnesota Cancer Center.
*Correspondence to: Julie A. Ross, Division of Population Sciences,
University of Minnesota Cancer Center, MMC 422, 420 Delaware St.
S.E., Minneapolis, MN 55455. E-mail: firstname.lastname@example.org
Received 18 June 2007; Accepted 18 June 2007
a challenge to have samples (e.g., cord blood, meconium) collected
prospectively for studies of childhood leukemia. Some large
international birth cohorts, including the National Childrens Study
in the United States, have considered whether combining forces
might help to address childhood cancer questions such as this .
Secondly, the observation of a depletion in the number of affected
AML1-ETO cells supports the contention that other events, whether
environmental and/or endogenous, need to occur in order for
leukemia to develop. It would also be of interest for the investigators
to explore potential associations with TEL-AML1 using similar
methods. Overall, the investigators are to be commended on a well-
done and thoughtful study that reinforces the need to investigate
observed associations from questionnaire data in other settings
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2. MaX,Buffler PA,Gunier RB, et al. Critical windows of exposure to
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3. Rowley JD. Seminars from the University of Minnesota Chromo-
some translocations: Dangerous liaisons. J Lab Clin Med 1998;
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Pediatr Blood Cancer DOI 10.1002/pbc