Pediatr Blood Cancer 2007;49:607–608

HIGHLIGHTby Julie A. Ross, PhD

1,2*

Looking for Leukemia Clues in of all Places. . . :Meconium!(Commentary on LaFiura et al., pp. 624–628)

B ecause of the rarity of childhood cancer, epidemiologists

necessarily rely on the case-control approach. In these

studies, 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 1–15 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 [5]. 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 [8–10]. 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 [13]. These

observations provide strong evidence that additionalmutationsmust

occur before leukemia develops in most children.

In this issue, Ge Yet al. [14] report on an elegant pilot study that

examines correlations between specific pesticides present in

meconium (i.e., an infant’s 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 infant’s 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

child’s 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 maternal–fetal 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,

Minnesota

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: ross@epi.umn.edu

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 Children’s Study

in the United States, have considered whether combining forces

might help to address childhood cancer questions such as this [15].

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

whenever possible.

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Pediatr Blood Cancer DOI 10.1002/pbc

608 Ross