Spontaneous rupture of colon cancer, combined with psoas abscess formation, is rare. A 44-year-old male visited for back pain and left buttock mass. Abdominal computed tomography and magnetic resonance image revealed a large abscess in the left psoas muscle and in the left lower quadrant area. Ten days after incision and drainage, a skin defect around the left anterior superior iliac spine remained. A local flap was performed using a superficial skin graft. Ten days after the stitches had been removed, fecal discharge was observed around the anterior superior iliac spine at the flap site. An operation was performed by a general surgeon who had diagnosed this as a case of enterocutaneous fistula. Operative findings included a ruptured tumor mass in the descending colon, which was connected to a retroperitoneal abscess. Pathologic report findings determined adenocarcinoma of the resected colon. Herein, we report a case of psoas abscess resulting from perforating colon cancer
