PIK3CA mutation in a mixed dysembryoplastic neuroepithelial tumor and rosette forming glioneuronal tumor, a case report and literature review

Rosette forming glioneuronal tumors are rare, World Health Organization (WHO) grade I novel tumors frequently affecting the fourth ventricle or posterior fossa with typical neuronal pseudorosettes. RGNTs have been described as possessing additional histologic features of DNETs or pilocytic astrocytomas. Activating PIK3CA mutations have been identified as recurring genetic event in RGNTs. We report a 35year old man who presented with binocular diplopia, headache, and was found to have a third ventricle tumor. Tumor pathology and oncogene evaluation were conducted. The tumor demonstrated histologic features consistent with mixed RGNT/DNET. Genetic studies revealed a PIK3CA mutation in exon 9 (E545K, C. 1633G>A) without IDH1, p53, 1p19q chromosomal co-deletion, or BRAF mutations. A literature search revealed six cases of PIK3CA mutations in RGNTs and seven cases of mixed RGNT/DNET. No cases of mixed RGNT/DNET with a PIK3CA mutation have been described. This is the first documented case of an RGNT/DNET with an activating PIK3CA mutation. The presence of a PIK3CA mutation aids histologic classification in the setting of mixed histology, and may have implications for targeting the PI3K/AKT/mTOR pathway in this tumor type. •Mixed RGNT and DNET are a rare brain tumor commonly found in the posterior fossa with the histologic features of both tumor types.•Detailed genetic analyses of RGNT are rare and the most common mutation is the PIK3CA mutation of the PI3K/Akt/mTOR pathway.•Documented genetic analyses of mixed RGNT/DNET are limited and have not tested for the PIK3CA mutation.•This is the first documented case of the PIK3CA mutation in mixed RGNT/DNET; however it is possible that the PIK3CA mutation is common in this rare tumor subtype based on its prevalence in RGNT.•Identification of the PIK3CA mutation in RGNT and RGNT/DNET may have therapeutic implications for chemotherapy targeting the PI3K/Akt/mTOR pathway.