Acute Appendicitis due to Rare Metastasis From Lung Cancer: A Case Report.

Gastrointestinal metastasis from primary lung cancer is uncommon and metastasis to the appendix is particularly rare. It often presents with symptoms of acute appendicitis or remains asymptomatic, leading to incidental diagnosis. We report a rare case of lung cancer with metastasis to the appendix presenting as acute appendicitis. A 74-year-old male patient with a history of severe COPD was diagnosed with advanced-stage lung cancer and had been receiving targeted therapy for over a year. He subsequently developed acute appendicitis and underwent an appendectomy. Histopathological examination of the appendix revealed adenocarcinoma infiltrating the serosa of the appendix and immunohistochemistry staining was consistent with a primary adenocarcinoma lung cancer. Metastasis of lung cancer to the appendix is an extremely rare occurrence. This case highlights the diverse clinical manifestations in patients with metastatic lung cancer and underscores the importance of considering differential diagnoses for the aetiology of acute appendicitis, as it may be secondary metastasis.