Cushing's syndrome due to atypical carcinoid of the mediastinum.

Ectopic Cushing's syndrome, caused by a neuroendocrine tumor (NET), is a rare finding. NETs of the mediastinum are extremely rare. NETs arising from the anterior mediastinum are generally aggressive. They are widely characterized at clinical presentations, and may be asymptomatic or present with atypical symptoms. Prognosis is often poor due to their local recurrence and distant metastasis despite a multimodal approach. A 33-year-old male patient was admitted to our department with a femoral soft tissue abscess, diabetes, and hypokalemia. He had no typical features of Cushing's syndrome. However, with a few simple tests, that is, a basal hormone profile, and low-dose and high-dose dexamethasone suppression tests, we diagnosed this complicated condition of ectopic adrenocorticotrophic hormone (ACTH) secretion. Thoracic computed tomography revealed an anterior mediastinal mass of 35 × 22 mm. A surgical excision of the tumor was proposed, and intra-operative pathology consultation returned positive for the suspected NET. Immunohistochemically, the tumor cells were positive for CK, CD56, Chromogranin, Synaptophysin, S100, and CD117. No thymic tissue was found. The Ki-67 was 4%. A diagnosis of primary NETs of the mediastinum, intermediate grade (G2), of atypical carcinoids according to WHO 2015 was established. This patient survived with no sequelae, no distant metastasis, no recurrence, and without adjuvant radiotherapy or chemotherapy 2 years after surgery thanks to earlier diagnosis and prompt surgical intervention. Mediastinum ectopic ACTH-secreting tumors are a rare type of cancer. According to recent research, these tumors frequently display more aggressive behavior and are linked to endocrinopathies. It is noted that patient might have a better outcome and a longer survival time due to earlier detection and complete resection of malignancies.