Rectal metastasis from lung cancer diagnosed by endoscopic ultrasound‐guided fine needle biopsy: A case report

A 73-year-old man visited our hospital due to hyperintestinal peristalsis and diarrhea. He had been undergoing regular annual checkups for dust lung disease. Contrast-enhanced computed tomography scan showed edematous thickening of the rectal wall with contrast effect. A colonoscopy revealed a submucosal tumor-like protrusion in the Rb lesion of the rectum without neoplastic epithelial changes. Forceps biopsies of the overlying mucosa were non-diagnostic; however, endoscopic ultrasound-guided fine needle biopsy revealed that the specimen was poorly differentiated non-small cell invasive carcinoma. Then, we performed a chest computed tomography and a newly detected mass lesion in the upper lobe of the right lung. Based on immunohistochemical analysis and image findings, the patient was diagnosed with rectal metastasis from lung cancer. Subsequently, sputum cytology confirmed the diagnosis of lung adenocarcinoma. Rectal submucosal tumor-like protrusions are occasionally encountered. When a non-exposed rectal tumor is identified, it is important to differentiate metastatic diseases, consider endoscopic ultrasound-guided fine needle biopsy, and make a definitive diagnosis through detailed immunohistochemical evaluation and systemic imaging surveillance.