USP8 and TP53 drivers are associated with CNV in a corticotroph adenoma cohort enriched for aggressive tumors

Context: Pituitary corticotroph adenomas are rare tumors that can be associated with excess adrenocorticotropic hormone (ACTH) and adrenal cortisol production, resulting in the clinically debilitating endocrine condition Cushing disease. A subset of corticotroph tumors behave aggressively, and genomic drivers behind the development of these tumors are largely unknown.

Objective: To investigate genomic drivers of corticotroph tumors at risk for aggressive behavior.

Design: Whole-exome sequencing of patient-matched corticotroph tumor and normal DNA from a patient cohort enriched for tumors at risk for aggressive behavior.

Setting: Tertiary care center.

Patients: 27 corticotroph tumors from 22 patients analyzed. 12 tumors were macroadenomas, of which 6 were silent ACTH tumors, 2 were Crooke's cell tumors, and 1 was a corticotroph carcinoma.

Intervention: Whole-exome sequencing.

Main outcome measure: Somatic mutation genomic biomarkers.

Results: We found recurrent somatic mutations in USP8 and TP53 genes, both with higher allelic fractions than other somatic mutations. These mutations were mutually exclusive, with TP53 mutations occurring only in USP8-wildtype (WT) tumors, indicating they may be independent driver genes. USP8-WT tumors were characterized by extensive somatic copy number variation compared to USP8-mutated tumors. Independent of molecular driver status, we found an association between invasiveness, macroadenomas, and aneuploidy.

Conclusions: Our data suggest that corticotroph tumors may be categorized into a USP8-mutated, genome-stable subtype versus a USP8-WT, genome-disrupted subtype, the latter of which has a TP53-mutated subtype with high level of chromosome instability. These findings could help identify high risk corticotroph tumors, namely those with widespread CNV, that may need closer monitoring and more aggressive treatment.