The patient was a 61-year-old man who visited the emergency department of our hospital for the exacerbation of left lower abdominal pain. CT scan revealed a tumor in the descending colon and fluid accumulation and extensive foamy gas in the retroperitoneal space, suggesting that the tumor in the descending colon penetrated the parietal peritoneum and formed an abscess. After percutaneous drainage for the retroperitoneal abscess, a transverse colostomy was performed. After the improvement of the general conditions, the patient underwent an endoscopic biopsy and was diagnosed with well-differentiated adenocarcinoma. After 4 courses of FOLFOX plus panitumumab(PANI), with the drainage and wound care continued, he was discharged and underwent 2 additional courses of chemotherapy. PET-CT revealed marked shrinkage of the descending colon tumor without distant metastasis. Therefore, left colectomy and transverse colostomy closure were performed as curative surgeries. After discharge, the patient underwent 6 courses of chemotherapy and has been followed up without recurrence for 13 months after the curative surgeries.