PET scans can often detect a tumor that can't be seen on CT scans or regular X-rays. Cancer tumors grow rapidly and so actively metabolize glucose. In a PET scan, the patient is injected with glucose containing a radioactive tracer. The PET scan image shows areas of the body that utilize the glucose. The brain, heart, and bladder all metabolize glucose and appear black in the image, along with any cancer tumors that are present.

When recurrent colorectal cancer is caught and treated in its early stages, the vast majority of patients survive more than 5 years and are considered cured. That's why follow-up after initial treatment is important. Recurrent cancer is diagnosed using a number of tests, including blood tests, ultrasounds, bone scans, chest X-rays, and CT, PET, or MRI scans. Depending on what is found, a new treatment plan will be decided on.