Global Report on Nutrition's Role in Cancer Prevention Will Adopt New Approach

American Institute for Cancer Research
Tuesday, 11 November 2003

Comprehensive "Portfolio Method" to Evaluate Mounting Scientific Evidence, Giving Consideration to All Study Types

Speaking today before an audience of international health policy makers and members of the world scientific community, Geoffrey Cannon representing the World Cancer Research Fund International (WCRF International) announced that an upcoming global report on nutrition, physical activity and cancer prevention will employ an innovative method to review the scientific evidence as objectively as possible.

Work has officially begun on the production of the 2nd WCRF/AICR Expert Report, Cannon said. Due in 2006, the report will evaluate the many thousands of published, peer-reviewed scientific studies that have investigated how factors related to food, nutrition and physical activity affect the chances of developing cancer.

The WCRF/AICR Expert Panel has adopted a "portfolio" approach to the science, Cannon said. Essentially, a portfolio approach endeavors to consider evidence from different kinds of scientific studies without favoring one type over another.

In so doing, it differs from other methods that have been used in the past to evaluate scientific data. Such methods consider evidence from randomized controlled trials (RCTs) to be the "gold standard" that supersedes evidence from other study types.

Portfolio Approach Enables a More Comprehensive Understanding

The decision to employ a portfolio approach in the 2nd Expert Report, Cannon said, was dictated by the need to address questions about overall diet and cancer development that short-term clinical studies like RCTs are simply not designed to answer.

"RCTs are excellent tools for determining the effectiveness of a cancer treatment – their precise focus allows them to measure how well a single substance such as a new cancer drug affects an already existing cancer. When it comes to cancer prevention, however, the questions researchers must ask are wholly different, involve a host of interrelated factors and are considerably more complex. That is why, for questions of prevention, the 2nd WCRF/AICR Report will consider RCTs one important source of data, but not more important than other sources."

RCTs are generally short-term interventions, lasting anywhere from a few days to as long as five years. But cancer is a disease that develops slowly, over many years and even decades. Also, RCTs that involve dietary factors typically administer isolated food substances at doses considerably higher than would be found in the diet.

The portfolio approach used in the 2nd WCRF/AICR Expert Report will consider evidence from RCTs alongside evidence from other study types, including:

• studies that compare the pre-existing diets and cancer rates of entire countries or regions (population studies)
• studies that compare how cancer rates change when individuals eating a traditional regional diet move to a new country or region and adopt the local diet (migration studies)
• studies that compare the diets a group of cancer patients ate in the years before diagnosis to the diets eaten in the same time period by a group of statistically similar individuals who are still cancer-free (case-control studies)
• studies that track the existing diets and cancer rates of large groups of individuals over several years (cohort studies)

Experimental Studies Vital to Complete the Picture

A review of the above epidemiological evidence might be enough to suggest that certain diet and lifestyle factors are associated with cancer risk. But the 2nd WCRF/AICR Expert Report will also seek to pinpoint those specific aspects of diet and physical activity that exert a direct influence over the cancer process.

"Experimental studies that involve cells, tissues and animal models are also vital to a comprehensive understanding of the diet-cancer link. If epidemiological studies identify a factor that may be associated with cancer risk, it's an important finding. But if that same factor can be observed to affect the cancer process on a direct cellular, molecular or genetic level, especially if the mechanism of action is shown to operate in humans, the evidence of its role becomes considerably stronger," said Cannon.

This search for such plausible biological connections between what we eat and do and the development of cancer will lead the Expert Panel to consider additional evidence from:

• Metabolic studies that establish ways to measure certain short-term changes in the human body (such biomarkers as levels of nutrients/ phytochemicals in the blood or the existence of pre-cancerous polyps) that can "stand in for" longer-term changes (such as extended dietary change or colon cancer)
• Studies that test the effects of specific dietary factors on cancers that occur in complex living systems (animal models or in vivo studies)
• Studies that test the effects of specific dietary factors on the cancer process itself (in vitro studies)

When evidence from all of these different kinds of studies is weighed together in a systematic way, a fuller understanding of the connections between diet (including nutrition, physical activity and weight management) and cancer will develop. The goal of the 2nd WCRF/AICR Expert Panel Report is to objectively determine what the preponderance of evidence dictates about food, nutrition, physical activity and the prevention of cancer.

Cannon's remarks were delivered at a symposium sponsored by WCRF and its US affiliate, the American Institute for Cancer Research (AICR), as well as the US National Cancer Institute. The symposium took place during a conference of the Society for Latin American Nutrition.

For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org