Primary Co-Occurrence of Gonadal and Extragonadal Central Nervous System (CNS) Germ Cell Tumors (GCTs): Case Report and Review of the Literature

Background: The primary co-occurrence of gonadal and extragonadal central nervous system (CNS) germ cell tumors (GCTs) has rarely been reported in the literature, and a common opinion on the underlying etiopathogenetic mechanism is lacking. Objective: We aim to investigate the pathophysiological mechanisms and genetic pathways underlying the primary co-occurrence of gonadal and CNS GCTs. Methods: We reviewed data from 29 consecutive patients with a diagnosis of CNS GCT, evaluated in our Hospital over the past 23 years, and searched for those who had at least a primary gonadal co-occurrence of GCT. A systematic review of the literature according to the PRISMA guidelines was also conducted. For a comprehensive and detailed search, PubMed, Ovid MEDLINE, and Ovid EMBASE databases have been consulted. Boolean operators and MeSH terms were used to find studies. Only articles published between 2000 and 2023 were considered. Results: Including our Institutional case report, a total of 7 patients with both testicular NGGCTs and CNS GCTs were identified (5 patients with metachronous tumors and patients with synchronous presentation). The average age at tumor diagnosis was 17 years. The cerebral histotypes reported were mixed GCTs (3 cases; 43%), pure germinomas (3 cases, 43%), and one yolk sac tumor (14%). Two out of seven cases (29%) were syndromic, one suffering from Down Syndrome and the other from Testicular Dysgenesis Syndrome. Regarding the etiology and molecular mechanism of GCT development, several gene mutations have been reported in the literature. Particularly, genetic alterations in the MAPK and/or PI3K/AKT/mTOR pathway, together with mutations of the KIT gene, have been shown to guarantee survival and transformation of mismigrated totipotent primordial germ cells, while suppressor genes allow their resistance against apoptotic death. Aberrant chromosomes have also been reported to be responsible for oncogenic transformation. It is also known that CNS and testicular GCTs share some genetic/epigenetic profiles. Conclusions: The primary co-occurrence of testicular NGGCT and extragonadal CNS GCTs is extremely rare. Genetic factors seem to play a paramount role in their etiopathogenesis. Additional research is needed to elucidate molecular mechanisms of oncogenesis in such patients.