Abstract
A 77-year-old man was abmitted to our hospital for abdominal pain and rectal mass. He had no hematochezia and no lower urinary tract symptoms. Digital examination of the rectum revealed hard mass of the left side of the rectum. CT image of the pelvis showed marked thickening of the rectal wall and slightly enlarged lymph nodes around the sigmoid colon. Colonoscopy revealed small depressed lesions like type 0-IIc colonic cancer at the sigmoid colon and protruded lesion like submucosal tumor at the rectum. Pathological findings showed poorly differentiated adenocarcinoma on both lesions. So we diagnosed colorectal cancer and surgical procedure was planned. But pathologist suggested to us that this lesion might be metastatic prostate cancer. We added measuring of serum prostate specific antigen (PSA) level and immunohistochemical study. Serum PSA was very high (2,162ng/ml) and immunohistochemical staining of PSA was positive. MRI imaging of the pelvis showed no infiltration to the rectum, so he was diagnosed as prostate cancer and colorectal metastasis. Anti-androgen therapy was started immediately. Colorectal involvement/metastasis by prostate carcinoma is rare but endoscopist should aware of this pit fall of differential diagnosis.
