Regression of metastatic colon tumour from primary adenocarcinoma of the lung due to fistulisation to the bowel lumen

An 80-year-old Japanese male was diagnosed with pulmonary adenocarcinoma. The patient exhibited extensive extra pulmonary involvement in the bone, adrenal gland, abdominal lymph nodes, and sigmoid colon. A single course of chemotherapy with carboplatin and pemetrexed was administered as the first-line treatment. Subsequently, the patient received pemetrexed monotherapy. Two months after the diagnosis, rapid regression of the metastatic tumour in the sigmoid colon was observed. Based on the findings of CT scanning and colonoscopic examination, tumour-bowel fistulisation was considered to be a cause of the rapid regression. This case report illustrates a tumour-bowel fistula of a colonic metastatic tumour in a patient with lung cancer. Radiographic and endoscopic features of the rare manifestation are presented.