IDH1 immunohistochemistry reactivity and mosaic IDH1 or IDH2 somatic mutations in pediatric sporadic enchondroma and enchondromatosis.

Mosaic somatic mutations in the isocitrate dehydrogenase 1/2 (IDH1/2) genes have been identified in most enchondromas by targeted mutation analysis. Next-generation sequencing (NGS), that may detect even low-level mosaic mutation rates, has not previously been applied to enchondromas. Immunohistochemistry using the H09 clone is routinely used as a surrogate for the common R132H IDH1 mutation in gliomas. We compared immunohistochemistry and NGS results in a series of 13 enchondromas from 8 pediatric patients. NGS identified a heterozygous IDH mutation in all enchondromas, showing identical mutation status in patients with multiple tumors assessed, thereby confirming somatic mosaicism. A majority of the tumors harbored an IDH1 mutation (p.R132H in 3 tumors; p.R132C in 4 tumors from 2 patients; p.R132L and p.R132G in one tumor each). A p.R172S IDH2 mutation was identified in 4 enchondromas, but not in the ependymoma from one patient with Ollier disease, who further displayed a heterozygous STK11 missense mutation. IDH mutation rates varied between 14% (indicative of mutations in 28% of the cells and of intratumoral mosaicism) and 45% (tumor content was close to 100%). Cytoplasmic H09 reactivity was observed as expected in tumors with an IDH1 p.R132H mutation; cross-reactivity was seen with the p.R132L variant. This first NGS study of pediatric enchondromas confirms that IDH mutations may occur in a mosaic fashion. STK11 gene mutations may provide insights in the development of multiple cartilaginous tumors in enchondromatosis, this tumor suppressor gene having been shown in animal models to regulate both chondrocyte maturation and growth plate organization during development.

Intensity modulated radiation therapy or stereotactic fractionated radiotherapy for infratentorial ependymoma in children: a multicentric study.

This study was to evaluate the treatment dosimetry, efficacy and toxicity of intensity modulated radiation therapy (IMRT) and fractionated stereotactic radiotherapy (FSRT) in the management of infratentorial ependymoma. Between 1999 and 2007, seven children (median age, 3.1 years) with infratentorial ependymoma were planned with either IMRT (3 patients) or SFRT (4 patients), the latter after conventional posterior fossa irradiation. Two children underwent gross total resection. Median prescribed dose was 59.4 Gy (range, 55.8-60). The median follow-up for surviving patients was 4.8 years (range, 1.3-8). IMRT (median dose, 59.4 Gy) and FSRT (median dose, 55.8 Gy) achieved similar optimal target coverage. Percentages of maximum doses delivered to the cochleae (59.5 vs 85.0% Gy; P = 0.05) were significantly inferior with IMRT, when compared to FSRT planning. Percentages of maximum doses administered to the pituitary gland (38.2 vs 20.1%; P = 0.05) and optic chiasm (38.1 vs 14.1%; P = 0.001) were, however, significantly higher with IMRT, when compared to FSRT planning. No recurrences were observed at the last follow-up. The estimated 3-year progression-free survival and overall survival were 87.5 and 100%, respectively. No grade >1 acute toxicity was observed. Two patients presented late adverse events (grade 2 hypoacousia) during follow-up, without cognitive impairment. IMRT or FSRT for infratentorial ependymomas is effective and associated with a tolerable toxicity level. Both treatment techniques were able to capitalize their intrinsic conformal ability to deliver high-dose radiation. Larger series of patients treated with these two modalities will be necessary to more fully evaluate these delivery techniques.