Key Points

• A cluster of childhood cancers (in children under 18) was investigated in the Sainte-Pazanne area (7 selected municipalities) in Loire-Atlantique between January 2015 and March 2019 by Santé publique France;

• The investigation was monitored through a process of dialogue with the community, within a monitoring committee in the Pays de la Loire region. An analysis of the expectations and knowledge mobilized by local stakeholders was conducted by Santé publique France and will be detailed in the final investigation report;

• An epidemiological investigation was conducted by Santé publique France among the 13 families identified within the study area. It was not intended to identify individual causes for each cancer but rather to identify a common factor, specific to this area, that could explain the cluster of cases and on which action could be taken. It revealed an excess of pediatric cancers in the area comprising the 7 municipalities over the 2015–2019 period. The number of pediatric cancers was twice as high as the average observed in France for this period and this geographic area;

• No risk factor specific to the area and documented in the scientific literature was shared by the children. Santé publique France concludes that the situation is consistent with a spatio-temporal cluster without an identified common cause. In the absence of a hypothesis regarding a common cause, no additional measures or testing are recommended locally;

• The interaction of individual and/or environmental factors (cocktail effect) cannot be ruled out, but given the current state of scientific knowledge, it is not possible to explore this hypothesis;

• Santé publique France recommends continuing to monitor all new pediatric cancers diagnosed in this area and is committed to mapping pediatric cancers in Loire-Atlantique in collaboration with the Loire-Atlantique and Vendée Cancer Registry. To improve understanding of environmental risk factors, Santé publique France is conducting nationwide epidemiological studies with its partners;

• Spatio-temporal clusters of pediatric cancers have long been known, both in France and abroad, yet their cause remains unexplained to this day, despite numerous studies. The causes are likely multifactorial, with hypotheses—environmental, genetic, and/or immuno-infectious—that remain under debate. In environmental health, epidemiological studies generally face weak associations between the disease and risk factors, which severely limits the ability of investigations to draw conclusions at the local level (due to insufficient sample size).