PET Scanning Detects Colorectal Cancer Recurrence Earlier

Routine monitoring with positron emission tomography (PET) scanning that detects alterations in the function of cells, achieves earlier detection of recurrences of colorectal cancer than traditional scanning, which simply visualizes the structure of body tissues, a prospective study has shown.

Colorectal cancer--cancer affecting the lower part of the digestive tract--is the second most common cause of cancer-related deaths in Western countries. Most individuals newly diagnosed with the disease undergo surgery to completely remove their tumor. However, about half of people who have curative surgery go on to develop recurrent disease. The median survival after surgery is two years. Adjuvant chemotherapy--anticancer drug treatment given just after surgery--improves the prognosis, but one-third of patients having this treatment still suffer a recurrence within two years after surgery.

Surgery to remove metastases in the liver or lung in people who have a recurrence of colorectal cancer improves survival so that 35-40% are alive after five years. This means that it is very important to monitor patients with colorectal cancer regularly to identify recurrence as early as possible so that tumor tissue can be removed and their odds of survival improved. Most people have regular clinical examinations and computed tomography (CT) scans, which provide detailed images of structures inside the body, to look for signs of recurrence.

French researchers performed a study to determine if functional positron emission tomography (PET) imaging, which looks at the function of body cells by measuring their use of a radio-labeled isotope of glucose (18-fluorodeoxyglucose, 18FDG)--could detect recurrences of colorectal cancer earlier than CT imaging. They randomly allocated 130 patients who had undergone curative surgery for colorectal cancer followed by chemotherapy to regular follow-up with conventional tests or with PET scans.

All the patients had six follow-up appointments, starting from the ninth month after their initial surgery and continuing to 24 months or their death. They had a physical examination, measurement of biologic markers for cancer, an ultrasound scan every 3 months (replaced by abdominal CT scans after 9 and 15 months), and a chest X-ray every 6 months. Patients in the PET group also had 18FDG-PET scans after 9 and 15 months.

Results showed that recurrence occurred in 46 patients--25 in the FDG-PET group and 21 in the group having conventional follow-up. Use of PET scans revealed unexpected tumors in an additional three patients.

Recurrences were detected after a significantly shorter time with PET scanning (12.1 months, on average) compared with conventional follow-up (15.4 months, p = 0.01). Recurrences in the PET group were also more frequently cured by surgery, with 10 patients with recurrence being cured, compared with only 2 patients in the group not having PET scans.

Prof. Iradj Sobhani, from the Université Paris 12 and Hôpital Henri Mondor (Paris, France), and lead author of the study, commented, "We showed that FDG-PET is a valuable adjunct to conventional follow-up. Using this new follow-up strategy increased the rate of curative resection by allowing us to detect recurrences of colorectal cancer at an earlier stage. Regular FDG-PET monitoring in the follow-up of colorectal cancer patients may permit the earlier detection of recurrence. We would expect improved patient survival if such as [a] follow-up program was undertaken.”

PET scanners have now been developed that can detect even smaller tumors than the system used in the French study. The investigators noted that combined PET-CT scans appeared to provide more accurate diagnoses than using the techniques separately. They predicted that using combined PET-CT scans would make it easier to accurately determine the stage of a patient's cancer, although more research is needed to validate this.

The study was published online February 26, 2008 in the British Journal of Cancer.


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Université Paris 12 and Hôpital Henri Mondor