Study of leukemias in children living close to heavily used roads

These results are published in the American Journal of Epidemiology.

Cancer affects over 1,700 children under 15 years of age every year in France, which has a population of a little over 11 million children. Surveillance of these cancers has been provided by the French National Registry of Childhood Haematopoietic Malignancies since 1990, and by the French National Registry of Childhood Solid Tumours since 2000. With 470 new cases each year, leukemias (blood cancers) are the most common childhood cancers, and are mainly acute lymphoblastic leukemias. "Myeloblastic" or "myeloid" leukemia is another type of leukemia, and affects myeloid stem cells, which give rise to the red blood cells. Today, 5-year survival following childhood leukemia is over 80%.

The general objective of the GEOCAP programme (GEOlocation Study of Paediatric CAncers) is to study the role of environmental exposures in the occurrence of cancer in children under 15 years.

One of the hypotheses of the research community is that there is an increased risk of leukemia in children living close to heavily used roads. The increased risk of myeloblastic leukemia for adults with a history of occupational exposure to benzene has long been known.

The EPICEA (Epidemiology of Childhood and Adolescent Cancers) team, directed by Jacqueline Clavel, Inserm Research Director, at CRESS, has reported the results of a study on the incidence of leukemias in children living close to heavily used roads. It is a case-control study that allowed the assessment of exposure level to one or more risk factors. All 2,760 cases of childhood leukemia diagnosed in metropolitan France between 2002 and 2007 were included in the study, and compared to a contemporary sample of 30,000 control children representative of the metropolitan population, and constituted in collaboration with the French National Institute of Statistics and Economic Studies (INSEE).

"The frequency of myeloblastic type leukemias was 30% higher in children living within a 150 m radius of heavily used roads, and where the combined length of road sections within this radius exceeded 260 m," explains Jacqueline Clavel, Inserm Research Director.

In contrast, there was no association between acute lymphoblastic leukemias -- the most common -- and the atmospheric concentration of nitrogen dioxide, distance or combined length of heavily used roads in the vicinity of dwellings.

The researchers particularly studied the case of the Île-de-France region of Paris, the most urbanised region, for which the mean annual concentration of benzene, mainly from road traffic, was estimated in the vicinity of each residence in the study in a particularly precise manner with the help of data modelled by Airparif, which is responsible for the monitoring of air quality in Île-de-France. They observed that the risk of childhood acute myeloblastic leukemia was double in Île-de-France children whose residences were the most exposed to traffic, i.e. when, simultaneously, the combined length of road sections within a 150 m radius of the residence exceeded 300 m, and the estimated mean annual concentration of benzene in the vicinity of the residence was above the median value observed in Île-de-France (1.3 µg/m3).

In keeping with the hypotheses on which the study is based, exposure to benzene related to car traffic might be one of the explanations for this association.