Second Malignancy Masquerading as Recurrence of Neuroendocrine Tumor.

Neuroendocrine tumors (NETs) may mimic many endocrine syndromes, including Cushing syndrome (CS) secondary to ectopic ACTH secretion. Radiotherapy (RT) is often used as adjuvant therapy for such persistent or recurrent NETs. However, RT may predispose a susceptible person to a second malignancy. Here, we reported the story of a 37-year-old male, who presented with progressive weight loss, bone pain, and shortness of breath in the emergency department. He was diagnosed with CS secondary to a carcinoid tumor in the bronchopulmonary tree a decade previous and underwent total bilateral adrenalectomy. He also underwent lobectomy, and subsequent RT for a primary NET and was in clinical remission. His presenting symptoms were considered a recurrence of pulmonary NETs. However, the biopsy suggested high-grade mucoepidermoid carcinoma (MEC). MEC of the lung is a rare tumor with a prevalence of <1% of all lung malignancies. MEC of the lung after RT for bronchial NET-causing ectopic CS has not yet been reported in the literature. The present patient did not survive despite achieving remission of CS and primary tumor because of the aggressive second malignancy attributed to RT, which was given for the primary tumor.