Abstract
INTRODUCTION AND IMPORTANCE: Metastasis of primary lung cancer to the small intestine is rare, and the prognosis is poor. Early diagnosis of small intestinal metastasis is difficult because the incidence of clinically obvious symptoms is low. CASE PRESENTATION: This report described a rare case of small intestine metastasis of lung adenocarcinoma. It is worth noting that the patient was diagnosed with lung adenocarcinoma (T2aN0M0, stage IB) over a year ago. However, he complained of fever, black stools, and abdominal pain for about a year after the surgery. Enhanced CT scans showed thickening of the intestinal wall and dilatation of the lumen in the right iliac area and adjacent pelvic cavity. Capsule endoscopy identified a space-occupying lesion with hemorrhaging in the ileum. A laparotomy was subsequently performed, and the histopathological confirmation revealed a metastatic lung adenocarcinoma and immunohistochemistry further showed positive results for TTF-1 and CK7. CLINICAL DISCUSSION: When patients with a history of primary lung cancer experience gastrointestinal symptoms, the possibility of distant metastasis of lung cancer to the digestive tract should be considered. CONCLUSION: Due to the rarity of primary lung cancer metastasis to the small intestine, we report the case of a 64-year-old male who presented with symptoms of gastrointestinal bleeding and was ultimately diagnosed with metastasis of primary lung cancer to the small intestine. When patients with lung cancer present with gastrointestinal symptoms, we cannot rule out the possibility of distant metastasis from primary lung cancer, although this possibility is unlikely.