A 50-year-old man presented with a 6-week history of lumbosacral back pain and altered bowel habit without hematochezia. Abdominopelvic computed tomography (CT) revealed a 5-cm rectal mass with obliteration of the fat plane between the mass and the tip of the coccyx that was interpreted as representing a neoplasm(●" Fig.1a). Followinganormal digital rectal exam, colonoscopy revealed a subtle po...