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SST5 expression and USP8 mutation in functioning and silent corticotroph pituitary tumors
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Edité par CCSD ; BioScientifica Ltd. -
International audience. Objective Somatostatin receptor type 5 (SST5) is inconsistently expressed by corticotroph tumors, with higher expression found in corticotropinomas having ubiquitin-specific protease 8 ( USP8 ) mutations. Aims were to study the correlation between characteristics of corticotropinomas and SST5 expression/ USP8 mutation status and to describe the response to pasireotide in five patients. Design Retrospective cohort study. Methods Clinico-biochemical, radiological and pathological data of 62 patients, operated for a functioning or silent corticotropinoma between 2013 and 2017, were collected. SST5 expression was measured by immunohistochemistry (clone UMB-4, Abcam, IRS > 1 being considered positive), and Sanger sequencing was performed on 50 tumors to screen for USP8 mutations. Results SST5 expression was positive in 26/62 pituitary tumors. A moderate or strong IRS was found in 15/58 corticotropinomas and in 13/35 functioning corticotropinomas. Among functioning tumors, those expressing SST5 were more frequent in women (22/24 vs 9/15, P = 0.04) and had a lower grade ( P = 0.04) compared to others. USP8 mutations were identified in 13/50 pituitary tumors and were more frequent in functioning compared to silent tumors (11/30 vs 2/20, P = 0.05). SST5 expression was more frequent in USP8 mut vs USP8 wt tumors (10/11 vs 7/19, P = 0.007). Among treated patients, normal urinary free cortisol levels were obtained in three patients (IRS 0, 2 and 6), while a four-fold decrease was observed in one patient (IRS 4). Conclusion SST5 expression appears to be associated with functioning, USP8 mut and lower grade corticotropinomas. A correlation between SST5 expression or USP8 mut and response to pasireotide remains to be confirmed.
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