A Rare Presentation of Small Bowel Perforation Secondary to Microscopic Metastasis of Non-small Cell Lung Cancer (NSCLC): A Case Report.

Gastrointestinal tract perforation (GITP) due to metastatic lung cancer is an exceptionally rare occurrence. Symptoms can range from mild abdominal discomfort to severe and life-threatening bowel perforation. In this case presentation, we describe an unusual instance involving squamous non-small cell lung cancer (NSCLC), where microscopic metastases in the small bowel led to bowel perforation. Our patient, a 71-year-old male with a history of stage IIIa squamous cell carcinoma in the right lung and smoking history, completed chemoradiation therapy and is currently undergoing treatment with durvalumab. He presented to the ED with complaints of abdominal pain, nausea, and abdominal distention. His review of systems revealed no other significant issues, and his vital signs were stable. However, the abdominal examination revealed noticeable distention with tenderness upon palpation and guarding. Laboratory results were significant for leukocytosis with a left shift of neutrophils and mildly elevated kidney function. A CT scan of the abdomen and pelvis revealed widespread pneumoperitoneum, indicating a bowel perforation. Consequently, the patient underwent an urgent exploratory laparotomy, during which a small bowel perforation measuring 0.6 cm x 0.3 cm in the jejunum was identified, necessitating the resection of the affected bowel segment. Intraoperative esophagogastroduodenoscopy (EGD) showed normal findings. The histopathological examination of the resected bowel revealed clusters of squamous cell carcinoma with a desmoplastic reaction, affecting the submucosal and muscular layers at the site of the defect, with surgical margins free of tumor or inflammation. This finding indicated metastatic disease originating from the known lung squamous cell carcinoma. After the operation, the patient was admitted to the ICU due to septic shock caused by