LAUSR

BACKGROUND Corticotroph adenomas are immunopositive for adrenocorticotrophic hormone (ACTH) associated with elevated blood ACTH levels leading to Cushing disease (CD). Yet silent ACTH adenomas (SCA) immunostain for ACTH but do not cause hypercortisolism. SCA have consistently been shown to have a more aggressive postoperative course, then nonfunctioning and ACTH adenomas. Here we show that genome-wide methylation profiles can be used to distinguish ACTH adenomas from SCA. METHODS16 SCA patients and 19 CD patients that underwent transsphenoidal resection were included. Tumor size was measured by MRI. Tumor histology was proven by immunstain for ACTH and routine histopathology. Sanger sequencing was performed to analyse mutational burden within the ACTH locus (n=3). Genome-wide DNA methylation profiling was performed using a 850k Illumina EPIC array and classified by the DKFZ brain tumor classifier as well as PCA analysis using R (n=17). RESULTS Mean age was 55,4 and 46,2 for SCA and CD patients, respectively. Patients with SCA had significantly larger tumors (SCA: 12,56±3,07ccm; CD: 1,9±1,2ccm p< 0.01). Both SCA and CD tumors showed strong expression of ACTH as proven by immunohistochemistry. Sanger sequencing revealed no mutations within the ACTH gene locus in SCA. Both, SCA and CD tumors classified as ACTH adenomas by genome-wide methylation profiling. Further PCA of DNA methylation profiles allowed subtype tumor classification into SCA and CD adenomas. CONCLUSION SCA show a strong expression of ACTH without causing hypercortisolism. The reason for this is not yet known. Our data suggest that SCA do not harbor specific mutations within the ACTH gene locus. However genome wide methylation profiles allows subgrouping of SCA and CD adenomas.