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X-inactive–specific transcript (XIST) is one of the firstly discovered long non-coding RNAs with prominent roles in the process of X inactivation. Moreover, this transcript contributes in the carcinogenic process in different tissues. In addition to interacting with chromatin modifying molecules, XIST can be served as a molecular sponge for miRNAs to modulate expression of miRNA targets. Most of the studies have indicated an oncogenic role for XIST. However, in prostate cancer, a single study has indicated a tumor suppressor role for this lncRNA. Similar result has been reported for XIST in oral squamous cell carcinoma. In hepatocellular carcinoma, breast cancer, ovarian cancer, osteosarcoma, and renal cell carcinoma, different studies have reported inconsistent results. In the present manuscript, we review function of XIST in the carcinogenesis.

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Background Cushing’s disease (CD) is among the most common etiologies of hypercortisolism. Magnetic resonance imaging (MRI) is often utilized in the diagnosis of CD, however, up to 64% of adrenocorticotropic hormone (ACTH)-producing pituitary microadenomas are undetectable on MRI. We report 15 cases of MRI negative CD who underwent surgical resection utilizing a purely endoscopic endonasal approach. Methods Endoscopic endonasal transsphenoidal surgery (EETS) was performed on 134 CD cases by a single surgeon. Fifteen cases met inclusion criteria: no conclusive MRI studies and no previous surgical treatment. Data collected included signs/symptoms, pre- and post-operative hormone levels, and complications resulting from surgical or medical management. Data regarding tumor diameter, location, and tumor residue/recurrence was obtained from both pre- and post-operative MRI. Immunohistochemistry was performed to assess for tumor hormone secretion. Results Aside from a statistically significant difference (P = 0.001) in histopathological results between patients with negative and positive MRI, there were no statistically significant difference between these two groups in any other demographic or clinical data point. Inferior petrosal sinus sampling (IPSS) with desmopressin (DDAVP®) administration was performed on the 15 patients with inconclusive MRIs to identify the origin of ACTH hypersecretion via a central/peripheral (C/P) ratio. IPSS in seven, five and three patients showed right, left, and central side lateralization, respectively. With a mean follow-up of 5.5 years, among MRI-negative patients, 14 (93%) and 12 patients (80%) achieved early and long-term remission, respectively. In the MRI-positive cohort, over a mean follow-up of 4.8 years, 113 patients (94.9%) and 102 patients (85.7%) achieved initial and long-term remission, respectively. Conclusions Surgical management of MRI-negative/inconclusive Cushing’s disease is challenging scenario requiring a multidisciplinary approach. An experienced neurosurgeon, in collaboration with a dedicated endocrinologist, should identify the most likely location of the adenoma utilizing IPSS findings, followed by careful surgical exploration of the pituitary to identify the adenoma.

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