Significant heterogeneity in the geographical distribution of diffuse grade II/III gliomas in France

Diffuse WHO grade II and III gliomas (DGII/IIIG) are rare tumors, with few specific epidemiological studies. We aimed at describing the geographical distribution of a homogeneous series of histologically confirmed DGII/IIIG, over a four-year period (2006–2009), at a national level. The methodology is based on a multidisciplinary national network already established by the French Brain Tumor DataBase and data collected directly from every neuropathology department. Personal home addresses were collected for confirmed cases. For each region, the incidence of DGII/IIIG was analyzed and standardized on the age and sex distribution of the French population. The number of patients with newly diagnosed, histologically confirmed DGII/IIIG was 4,790. The overall crude rate was 19.4/10⁶. To enable international comparisons, standardized rates were calculated as follows: 19.8/10⁶, 18.8/10⁶ and 16.0/10⁶ (reference population, Europe, US and world, respectively). The geographical distribution by region showed significant differences, with higher incidence rates in Northeast and central parts of France. This work is the first studying the geographical distribution of a pure series of DGII/IIIG at a national level. It demonstrates significant heterogeneity in the distribution, and raises the question of the role of environmental and/or genetic risk(s) factor(s) for DGII/IIIG.