This 65-year old man underwent surgical resection of his rectal cancer ten years ago. Following successful resection the patient received radiation therapy to his pelvis. The patient has a rising CEA level suggesting recurrent colorectal cancer. CT of the abdomen and pelvis showed chronic postoperative changes and no evidence of tumor.

The whole body FDG PET scan shows focal hypermetabolism in the presacral region indicative of neoplasm. No other abnormalities were identified.

A biopsy confirmed the PET finding of recurrent neoplasm and the patient's locally recurrent rectal cancer was completely resected. The patient received additional radiation therapy to the pelvis.

Cancer therapies, especially surgery and radiation therapy, leave residual scarring that can mask recurrent neoplasm when evaluated by CT. PET detects the hypermetabolism of tumors even in areas of treatment induced changes.