Clinical Identification of Oncogenic Drivers and Copy-Number Alterations in Pituitary Tumors.

Pituitary tumors are the second most common adult primary brain tumor, with a variable clinical course. Recent work has identified a number of genetic determinants of pituitary tumor subtypes, which may augment traditional histopathologic classification schemes. We sought to determine whether pituitary tumors could be stratified based on objective molecular characteristics using a clinical genomics assay. We performed a retrospective analysis of patients operated on at the Brigham and Women's Hospital from 2012 to 2016 whose pituitary tumors were profiled using multiplexed next-generation sequencing. We analyzed 127 pituitary tumors, including 114 adenomas, 5 craniopharyngiomas, and 8 tumors of other histologies. We observed recurrent BRAFV600E mutations in papillary craniopharyngiomas, CTNNB1 mutations in adamantinomatous craniopharyngiomas, and activating GNAS mutations in growth hormone-secreting adenomas. Furthermore, we validated the presence of two distinct genomic subclasses in adenomas (i.e., those with disrupted or quiet copy-number profiles) and the significant association of disruption with functional hormone status (P < 0.05). We report the clinical implementation of next-generation sequencing of pituitary tumors. We confirmed previously identified molecular subclasses for these tumors and show that routine screening as part of clinical practice is both feasible and informative. This large-scale proof-of-principle study may help to guide future institutional efforts for pituitary tumor classification as well as the incorporation of such techniques into prospective analysis as part of clinical trials.

Bi WL ，Greenwald NF ，Ramkissoon SH ，Abedalthagafi M ，Coy SM ，Ligon KL ，Mei Y ，MacConaill L ，Ducar M ，Min L ，Santagata S ，Kaiser UB ，Beroukhim R ，Laws ER Jr ，Dunn IF ... -  《-》

Genetic and Epigenetic Characterization of Growth Hormone-Secreting Pituitary Tumors.

Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characterized; apart from mutations in the stimulatory Gα protein (Gαs encoded by GNAS) causing activated cAMP synthesis, pathogenic variants are rarely found in growth hormone-secreting pituitary tumors (somatotropinomas). The purpose of the current work was to clarify how genetic and epigenetic alterations contribute to the development of somatotropinomas by conducting an integrated copy number alteration, whole-genome and bisulfite sequencing, and transcriptome analysis of 21 tumors. Somatic mutation burden was low, but somatotropinomas formed two subtypes associated with distinct aneuploidy rates and unique transcription profiles. Tumors with recurrent chromosome aneuploidy (CA) were GNAS mutation negative (Gsp- ). The chromosome stable (CS) -group contained Gsp+ somatotropinomas and two totally aneuploidy-free Gsp- tumors. Genes related to the mitotic G1-S-checkpoint transition were differentially expressed in CA- and CS-tumors, indicating difference in mitotic progression. Also, pituitary tumor transforming gene 1 (PTTG1), a regulator of sister chromatid segregation, showed abundant expression in CA-tumors. Moreover, somatotropinomas displayed distinct Gsp genotype-specific methylation profiles and expression quantitative methylation (eQTM) analysis revealed that inhibitory Gα (Gαi) signaling is activated in Gsp+ tumors. These findings suggest that aneuploidy through modulated driver pathways may be a causative mechanism for tumorigenesis in Gsp- somatotropinomas, whereas Gsp+ tumors with constitutively activated cAMP synthesis seem to be characterized by DNA methylation activated Gαi signaling. IMPLICATIONS: These findings provide valuable new information about subtype-specific pituitary tumorigenesis and may help to elucidate the mechanisms of aneuploidy also in other tumor types.

Välimäki N ，Schalin-Jäntti C ，Karppinen A ，Paetau A ，Kivipelto L ，Aaltonen LA ，Karhu A ... -  《-》

Genomic Alterations in Sporadic Pituitary Tumors.

Bi WL ，Larsen AG ，Dunn IF 《-》

Landscape of somatic mutations in sporadic GH-secreting pituitary adenomas.

Alterations in the cAMP signaling pathway are common in hormonally active endocrine tumors. Somatic mutations at GNAS are causative in 30-40% of GH-secreting adenomas. Recently, mutations affecting the USP8 and PRKACA gene have been reported in ACTH-secreting pituitary adenomas and cortisol-secreting adrenocortical adenomas respectively. However, the pathogenesis of many GH-secreting adenomas remains unclear. Comprehensive genetic characterization of sporadic GH-secreting adenomas and identification of new driver mutations. Screening for somatic mutations was performed in 67 GH-secreting adenomas by targeted sequencing for GNAS, PRKACA, and USP8 mutations (n=31) and next-generation exome sequencing (n=36). By targeted sequencing, known activating mutations in GNAS were detected in five cases (16.1%), while no somatic mutations were observed in both PRKACA and USP8. Whole-exome sequencing identified 132 protein-altering somatic mutations in 31/36 tumors with a median of three mutations per sample (range: 1-13). The only recurrent mutations have been observed in GNAS (31.4% of cases). However, seven genes involved in cAMP signaling pathway were affected in 14 of 36 samples and eight samples harbored variants in genes involved in the calcium signaling or metabolism. At the enrichment analysis, several altered genes resulted to be associated with developmental processes. No significant correlation between genetic alterations and the clinical data was observed. This study provides a comprehensive analysis of somatic mutations in a large series of GH-secreting adenomas. No novel recurrent genetic alterations have been observed, but the data suggest that beside cAMP pathway, calcium signaling might be involved in the pathogenesis of these tumors.

Ronchi CL ，Peverelli E ，Herterich S ，Weigand I ，Mantovani G ，Schwarzmayr T ，Sbiera S ，Allolio B ，Honegger J ，Appenzeller S ，Lania AG ，Reincke M ，Calebiro D ，Spada A ，Buchfelder M ，Flitsch J ，Strom TM ，Fassnacht M ... -  《-》

Novel Genetic Causes of Pituitary Adenomas.

Recently, a number of novel genetic alterations have been identified that predispose individuals to pituitary adenomas. Clinically relevant pituitary adenomas are relatively common, present in 0.1% of the general population. They are mostly benign monoclonal neoplasms that arise from any of the five hormone-secreting cell types of the anterior lobe of the pituitary gland, and cause disease due to hormonal alterations and local space-occupying effects. The pathomechanism of pituitary adenomas includes alterations in cell-cycle regulation and growth factor signaling, which are mostly due to epigenetic changes; somatic and especially germline mutations occur more rarely. A significant proportion of growth hormone- and adrenocorticotrophin-secreting adenomas have activating somatic mutations in the GNAS and USP8 genes, respectively. Rarely, germline mutations predispose to pituitary tumorigenesis, often in a familial setting. Classical tumor predisposition syndromes include multiple endocrine neoplasia type 1 (MEN1) and type 4 (MEN4) syndromes, Carney complex, and McCune-Albright syndrome. Pituitary tumors have also been described in association with neurofibromatosis type 1, DICER1 syndrome, and SDHx mutations. Pituitary adenomas with no other associated tumors have been described as familial isolated pituitary adenomas. Patients with AIP or GPR101 mutations often present with pituitary gigantism either in a familial or simplex setting. GNAS and GPR101 mutations that arise in early embryonic age can lead to somatic mosaicism involving the pituitary gland and resulting in growth hormone excess. Senescence has been suggested as the key mechanism protecting pituitary adenomas turning malignant in the overwhelming majority of cases. Here we briefly summarize the genetic background of pituitary adenomas, with an emphasis on the recent developments in this field. Clin Cancer Res; 22(20); 5030-42. ©2016 AACR SEE ALL ARTICLES IN THIS CCR FOCUS SECTION, "ENDOCRINE CANCERS REVISING PARADIGMS".

Caimari F ，Korbonits M 《-》