Activating FGFR1 Mutations in Sporadic Pheochromocytomas

Abstract

Introduction: Pheochromocytomas are neuroendocrine tumors of the adrenal glands. Up to 40% of the cases are caused by germline mutations in one of at least 15 susceptibility genes, making them the human neoplasms with the highest degree of heritability. Recurrent somatic alterations are found in about 50% of the more common sporadic tumors with NF1 being the most common mutated gene (20-25%). In many sporadic tumors, however, a genetic explanation is still lacking.

Materials and methods: We investigated the genomic landscape of sporadic pheochromocytomas with whole-exome sequencing of 16 paired tumor and normal DNA samples and extended confirmation analysis in 2 additional cohorts comprising a total of 80 sporadic pheochromocytomas.

Results: We discovered on average 33 non-silent somatic variants per tumor. One of the recurrently mutated genes was FGFR1, encoding the fibroblast growth factor receptor 1, which was recently revealed as an oncogene in pediatric brain tumors. Including a subsequent analysis of a larger cohort, activating FGFR1 mutations were detected in three of 80 sporadic pheochromocytomas (3.8%). Gene expression microarray profiling showed that these tumors clustered with NF1-, RET,- and HRAS-mutated pheochromocytomas, indicating activation of the MAPK and PI3K-AKT signal transduction pathways.

Conclusion: Besides RET and HRAS, FGFR1 is only the third protooncogene found to be recurrently mutated in pheochromocytomas. The results advance our biological understanding of pheochromocytoma and suggest that somatic FGFR1 activation is an important event in a subset of sporadic pheochromocytomas.

Fig. 1

Somatic hotspot mutations in FGFR1. a Overview of next-generation sequencing reads from the mutated sites in Integrative Genomics Viewer. Read bases that match the hg19 reference are displayed in gray, and mismatches are indicated with color coded alternate alleles (FGFR1 is oriented on the reverse strand; hence, the sequence is here the reverse complement to the transcribed sequence). b Validation of the mutations in the two tumor samples (64T and 40T) with Sanger sequencing (in the direction of transcription) and the corresponding sequences from blood samples

Fig. 2

Frequency of FGFR1 mutations indifferent cohorts. Flow diagram simplifying the process of initial discovery and validation of somatic FGFR1 mutations in sporadic pheochromocytomas (PCCs). * With regard to somatic FGFR1 mutations; # of somatic FGFR1 mutations

Fig. 3

Hierarchical clustering of tumors based on gene expression levels. Mutation status is indicated below the dendrogram, showing that tumors with FGFR1 mutations cluster together with those that have RET, NF1, or HRAS mutations. Whereas mutations in the known susceptibility genes were mutually exclusive, one mutation in the novel susceptibility gene, FGFR1, occurred in combination with a somatic MAX mutation