Life and death of molecular subclones in recurrent meningioma: A case study.

Meningiomas are the most common primary intracranial tumors, of which atypical meningiomas account for ~ 20%. A loss of NF2 has been proven to be an initial step for meningioma development; however, the role of non- NF2 alterations is unknown. Here we report a case of an atypical meningioma with a NF2 splice donor mutation and four recurrences. Using a custom NGS panel, further complex heterogenic molecular alterations were discovered. At first, one subclone of the initial tumor showed an additional PIK3CA variant, most likely of no pathogenic relevance. Then, the first and second recurrences no longer harbored the PIK3CA variant and no tumor heterogeneity was found. The tumor-driving NF2 mutation persisted, however. The latest, third recurrence showed a remarkable genetic heterogeneity with multiple, additional non- NF2 variants and a pathogenic PIKC3A mutation. In detail, one subclone showed a SUFU and two SMARCE1 variants. Another, geographically separate tumor subclone, in contrast, showed several different non- NF2 variants in SMO , PIK3CA and SUFU . Most important, one of the newly acquired PIK3CA alterations in the kinase domain (L1006F) is likely to be an additional tumor-driving mutation, which activates the PI3K-AKT-mTOR pathway. The reported genetic heterogeneity in meningiomas has been addressed in only a few studies. Although some of the detected variants in our case are expected to have biochemical consequences, these consequences are usually not likely to promote tumor development, when taking into account the suggested role of the altered proteins in tumorigenic pathways. However, the occurrence of a single oncogenic missense mutation in a subclone of the third recurrence may indicate a clonal change towards enhanced aggressiveness. Taken together, our case supports the need to perform in-depth studies to clarify the role of non- NF2 mutations for meningioma growth and development.