MPTH-31CO-EXISTENCE OF TWO TERT PROMOTER REGION SOMATIC POINT MUTATIONS IN A RECURRENT GLIOBLASTOMA

Abstract

BACKGROUND: Mutations in the promoter region of the telomerase reverse transcriptase gene (TERT) occur at a frequency of greater than 80% in primary GBM. The two most observed TERT promoter mutations in primary GBM, C250T and C228T, each create a de novo transcription factor consensus binding site, upregulating TERT mRNA expression, and are thought to occur in a mutually exclusive fashion. Here we describe the case of a recurrent GBM found to harbor both the C250T and C228T mutations. METHODS: A 57-year-old woman who presented with right hemiparesis and expressive dysphasia was found to have a left frontal contrast-enhancing tumor. She underwent subtotal resection, which revealed primary GBM, and went on to receive standard chemoradiation combined with intra-arterial and intravenous bevacizumab as part of an experimental protocol. She returned with disease progression ten months later and underwent second resection. Fresh tumor was preserved for histopathology, DNA extraction, and was cultured in both serum-free and adherent conditions. RESULTS: Sequencing of tumor DNA revealed that almost all cells harbored the C250T mutation, while a small fraction of cells harbored the C228T mutation. In adherent conditions at early passage, the C250T mutation continued to predominate while there was slight enrichment of C228T. Early and late passage spheres uniformly exhibited the C228T mutation, while C250T was undetectable. Late passage adherent cells exhibited only C228T and could form spheres when transferred into serum-free conditions. All cultures were genotyped and compared to the patient's germline DNA to exclude contamination. CONCLUSIONS: Our results suggest that ongoing convergent evolution gave rise to the C228T mutation in a clone of tumor cells that did not harbor the prevailing C250T mutation of the original tumor. The clone containing C228T exhibited greater proliferation and superior sphere-forming ability in vitro compared to clones containing C250T, and may have been selected through treatment.