Ectopic Cushing’s Syndrome in Advanced Small-Cell Lung Cancer (SCLC): Clinical Challenges and Therapeutic Insights

Background/Objectives: Ectopic Cushing’s syndrome (ECS) is a rare, life-threatening condition caused by uncontrolled ACTH secretion from tumors, most commonly small-cell lung cancer (SCLC). ECS is traditionally reported in 1–6% of SCLC cases; however, recent data suggest it may be much higher. This study compares the clinical presentation of SCLC-related ECS (ECS-SCLC) with other ECS etiologies and analyzes the diagnosis, treatment, and outcomes of ECS-SCLC. Methods: We retrospectively analyzed the records of 39 ECS patients diagnosed between 2000 and 2024 at a tertiary endocrinology center. Seven cases (18%) were due to SCLC. Diagnosis was based on clinical signs, biochemical testing, imaging, and histopathology. Results: ECS-SCLC patients (five men, two women; median age 61), compared to other ECS etiologies, had a shorter time to diagnosis (median 1 vs. 2 months; p = 0.03), worse general condition (ECOG 4 vs. 3; p = 0.01), greater muscle weakness (Lovett scale median 2[IQR 1–2] vs. 2[IQR 2–3]; p = 0.04), more severe hypokalemia (2.12 vs. 2.7 mmol/L; p = 0.03), and required higher potassium supplementation (200 vs. 120 mEq/day; p = 0.001). All ECS-SCLC patients experienced weight loss (median 5 kg). Cortisol-lowering therapy (metyrapone or osilodrostat) was initiated in six patients (mean initiation time 3.7 days), leading to clinical improvement. Oncological treatment (chemotherapy or radiotherapy) was administered in five patients after stabilization. The median follow-up time was 3 months. Conclusions: Early recognition of ECS-SCLC and a multidisciplinary approach are critical. Severe hypokalemia and muscle weakness should prompt timely evaluation for hypercortisolism. Cortisol-lowering therapy may improve clinical status and facilitate oncological treatment.