Regular monitoring with positron emission tomography (PET) scanning – which detects changes in the function of cells – achieves earlier detection of recurrences of colorectal cancer than conventional scanning that simply looks at 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 people newly diagnosed with the disease undergo surgery to completely remove their tumour. However, approximately 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 follow up patients with colorectal cancer regularly to detect recurrence as early as possible so that tumour tissue can be removed and their chances 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 carried out a study to see if functional positron emission tomography (PET) imaging – looking at the function of body cells by measuring their use of a radio-labelled isotope of glucose (18fluorodeoxyglucose, 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 biological markers for cancer, an ultrasound scan every three months (replaced by abdominal CT scans after 9 and 15 months) and a chest X-ray every six 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 tumours in a further 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 two patients in the group not having PET scans.

Professor Iradj Sobhani, Université Paris 12 et 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.” He added: “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 follow-up programme was undertaken.”

PET scanners have now been developed that can detect smaller tumours than the machine used in the French study. The study authors noted that coupled PET and CT scans appears to provide more accurate diagnoses than using the techniques separately. They predicted that using combined PET-CT scans would make it easier to correctly determine the stage of a patient’s cancer, although more research is needed to confirm this.

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Scientists have for the first time discovered that people with the same cancer susceptibility genes respond differently depending on their race. Their results are published in Nature Genetics* .

The team from the University of Edinburgh has shown that a genetic marker is associated with an increased the risk of colon cancer in Europeans, but not in the Japanese population. But this genetic variant was associated with a similar risk of rectal cancer in both populations.

While dietary differences are already well known to be important, this discovery shows for the first time that genetic factors might explain some of the differences in bowel cancer risk between populations**.

This is one in a series of Cancer Research UK funded studies searching for bowel cancer susceptibility genes. The international collaborative project has the long term aim to find a set of genetic markers that could be used to identify subgroups of the population with an increased risk of bowel cancer.

Lead author, Cancer Research UK’s Professor Malcolm Dunlop based at the Institute of Genetics and Molecular Medicine at the University of Edinburgh, said: “This is the first time that a race-specific effect has been found for a genetic marker. It’s an important step forward in our knowledge of the causes of bowel cancer, bringing us ever closer to a genetic test for those at high risk of the disease.

“It’s important to catch bowel cancer at an early stage when it’s more likely to be treated successfully.”

Prof Dunlop and his team looked at the complete genetic make up of over 33,000 people in seven different countries.

In a parallel study, also published today in Nature Genetics***, a team of researchers led by Professor Richard Houlston based at the Institute of Cancer Research and Professor Ian Tomlinson at Cancer Research UK’s London Research Institute , along with Professor Dunlop and Professor Campbell in Edinburgh, found two new gene variants that increase the risk of bowel cancer.

Cancer Research UK’s director of cancer information, Dr Lesley Walker, said: “Our understanding of the causes of bowel cancer is quickly increasing. We can now begin to explain the some of the difference in rates of the disease between populations through specific genes.

“This international collaboration has helped us appreciate the complexity of the genetics behind bowel cancer. This collaboration will continue to bring knowledge that will eventually allow us to test people with a family history of the disease, catching cancer earlier in those who are at the highest risk or preventing it all together.”

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