Characteristics of gliomas in patients with somatic IDH mosaicism.

IDH mutations are found in the majority of adult, diffuse, low-grade and anaplastic gliomas and are also frequently found in cartilaginous tumors. Ollier disease and Maffucci syndrome are two enchondromatosis syndromes characterized by the development of multiple benign cartilaginous tumors due to post-zygotic acquisition of IDH mutations. In addition to skeletal tumors, enchondromatosis patients sometimes develop gliomas. The aim of the present study was to determine whether gliomas in enchondromatosis patients might also result from somatic IDH mosaicism and whether their characteristics are similar to those of sporadic IDH-mutated gliomas. For this purpose, we analyzed the characteristics of 6 newly diagnosed and 32 previously reported cases of enchondromatosis patients who developed gliomas and compared them to those of a consecutive series of 159 patients with sporadic IDH-mutated gliomas. As was the case with sporadic IDH mutated gliomas, enchondromatosis gliomas were frequently located in the frontal lobe (54 %) and consisted of diffuse low-grade (73 %) or anaplastic gliomas (21 %). However, they were diagnosed at an earlier age (25.6 years versus 44 years, p < 0.001) and were more frequently multicentric (32 % versus 1 %, p < 0.001) and more frequently located within the brainstem than sporadic IDH mutated gliomas (21 % versus 1 %, p < 0.001). Their molecular profile was characterized by IDH mutations and loss of ATRX expression. In two patients, the same IDH mutation was demonstrated in the glioma and in a cartilaginous tumor. In contrast to sporadic IDH mutated gliomas, no enchondromatosis glioma harbored a 1p/19q co-deletion (0/6 versus 59/123, p = 0.03). The characteristics of gliomas in patients with enchondromatosis suggest that these tumors, as cartilaginous tumors, result from somatic IDH mosaicism and that the timing of IDH mutation acquisition might affect the location and molecular characteristics of gliomas. Early acquisition of IDH mutations could shift gliomagenesis towards the brainstem thereby mimicking the regional preference of histone mutated gliomas.