Zosia Chustecka

February 06, 2014

In launching the World Cancer Report 2014 earlier this week, the editors emphasized the need for prevention and highlighted lifestyle behaviors that lead to cancer, including smoking tobacco, drinking alcohol, overweight/obesity, and lack of exercise.

The report, issued by the International Agency for Research on Cancer (IACR), contains contributions from more than 250 scientists worldwide, many of them leading experts in their fields.

It offers a “timely update,” said Margaret Chan, MD, director-general of the World Health Organization (WHO). The report compiles the most up-to-date analysis of data on all aspects of cancer, and among the evidence presented are data showing the extent to which lifestyle behaviors contribute to cancer.

This is “a key reference tool that will find extensive use among scientists, public health workers, and governments in supporting the implementation of national and regional plans for cancer prevention and control,” Dr. Chan writes in the foreword.

The American Society of Clinical Oncology (ASCO) called for action in response to the report, highlighting a “need to deepen the global commitment to cancer prevention.”

“Decades of research have shown that cutting tobacco use is the single most powerful way to prevent many deadly cancers, especially in developing countries where smoking is most widespread. Tackling obesity, a key modifiable risk factor for many cancers, is another top prevention priority,” ASCO said in a statement. In the United States, 1 in 3 cancer deaths is related to obesity, poor nutrition, or physical inactivity, and the problem will only increase as more countries and regions adopt the diet and lifestyles of more economically developed economies.”

“We can take action, in part by making healthier choices in our own lives and helping our patients and their families do the same. But we also need to hold national and global leaders accountable for curbing tobacco use and encouraging and ensuring access to cancer treatment and prevention resources for everyone in need,” ASCO commented.

Tobacco Is Still Most Important

Tobacco, both smoked and smokeless, remains the world’s leading cause of cancer morbidity and mortality, the report notes.

Nearly 20% of the world’s adult population smokes, and worldwide tobacco is killing around 6 million people each year from a variety of smoking-related diseases, the report estimates.

Precise figures are given for the year 2000, when 4.38 million premature deaths globally were attributed to smoking, with causes listed as cardiovascular disease (1.69 million deaths), chronic obstructive pulmonary disease (0.97 million deaths), and lung cancer (0.85 million deaths).

It is not only lung cancer that is linked to smoking, however. Cigarette smoking has also been identified as a cause of many other cancer types, including sites where the smoke is directly deposited and distal sites reached by circulating tobacco smoke components.

The IACR and also the US Surgeon General have concluded that the relationship with smoking is causal for cancers of the nasal and oral cavities, hypopharynx, larynx, trachea, esophagus, lung, bronchus, bone marrow (leukemia), stomach, kidney, pancreas, ureter, uterus, bladder, and cervix. The IACR expands this list to also include paranasal sinuses, liver, colon, rectum, and ovary (mucinous), but says it is unclear if there is a link with breast cancer.

The good news here is that tobacco is now recognized as damaging to health, and control strategies are being introduced globally, backed by the WHO Framework Convention for Tobacco Control (in place since 2005).

Alcohol Still Under-recognized

Still under-recognized, and not acted on, is the association between drinking alcohol and cancer.

The IACR has labeled alcoholic beverages as “carcinogenic to humans” (and placed them in group 1, alongside ultraviolet light and chronic infection with hepatitis B). This classification was first made in 1988, and then confirmed in 2007 and 2010.

It explains that ethanol is metabolized to acetaldehyde, and it is this that has a genotoxic effect, although there may also be other mechanisms involved, including increased oxidative stress, increased estrogen concentrations, and changes in folate metabolism and DNA repair.

The agency says cancers caused by drinking alcoholic beverages include those of the oral cavity, pharynx, larynx, esophagus, liver, colorectum, and female breast.

It estimates that in 2010, alcohol-attributable cancers were estimated to be responsible for 337,400 deaths worldwide, predominantly among men and liver cancer.

This burden of alcohol-attributable cancer can be reduced through alcohol policy measures such as reduction of availability, increases in prices, and bans on marketing, the agency suggests.

So far, however, there has not been any action, and even IARC’s highlighting of the link between alcohol and cancer drew a rapid response from the International Scientific Forum on Alcohol Research, which emphasized the distinction between excessive alcohol use and moderate drinking.

It is not a distinction that the IACR makes, however. The agency states that “the relationship between alcohol consumption and cancer is monotonic and without threshold…. This means that any reduction in alcohol consumption will be beneficial for health through the reduction of cancer risk.”

But cancer is not the whole story, of course. There is a wealth of data suggesting that some alcohol consumption (especially wine) is beneficial for cardiovascular health, and also some evidence suggesting that moderate drinkers live longer than nondrinkers.

For example, as the Forum on Alcohol Research pointed out, the European Prospective Investigation Into Cancer and Nutrition (EPIC) study, which showed that cancer risk increases with alcohol consumption, also found that the overall risk for death was lower in moderate drinkers compared with nondrinkers. However, the EPIC researchers note that as far as cancer is concerned, the risk increases with every drink, so even moderate amounts of alcohol — such as a small drink each day — increases the risk.

Potential health benefits from moderate drinking are also often raised by doctors reacting to news about alcohol increasing the risk for cancer, as previously reported by Medscape Medical News, and were recently raised in a study that concluded that alcohol causes 1 in 30 cancer deaths in the United States. These authors concluded that “reducing alcohol consumption is an important and underemphasized cancer prevention strategy.”

It is noticeable that alcohol is not mentioned at all in the latest cancer-prevention campaign from the American Institute for Cancer Research. Noting that about one third of all cancer could be prevented by making changes to diet, weight, and physical activity, the new Cancer Prevention: Do Something is summarized as, “Eat well, move more, stay lean,” and adds, almost as an afterthought, “and of course, don’t smoke.”

Diet, Obesity, and Physical Activity

The IACR report says that additional research is needed on many aspects of diet and physical activity in relation to cancer, including the effects of these behaviors during childhood and early adulthood.

Nevertheless, it draws several conclusions, as follows:

• Excess body fat increases the risk for cancers of the esophagus, colon, pancreas, endometrium, and kidney, as well as postmenopausal breast cancer. The evidence for obesity increasing the risk for these cancers is “convincing,” the agency comments, and there is a dose–response relationship, so being overweight is less risky than being obese.
• Regular physical activity reduces the risk for multiple cancers by contributing to weight control, and also reduces the risk for colorectal and breast cancer by additional mechanisms. The general consensus among researchers is that exercise should be of moderate intensity and average at least an hour each day.
• High consumption of red meat, especially processed meat, is associated with a risk for colorectal cancer. 

“A diet high in fruit and vegetables and whole grains does not appear to be as strongly protective against cancer as initially believed,” the report notes. “However, this dietary pattern is still advisable because of the benefits for diabetes and cardiovascular diseases, and some possible reductions in cancer incidence.”

Strong Actions Needed

In an invited commentary in the report, Walter Willet, MD, professor of epidemiology and nutrition at the Harvard School of Public Health and professor of medicine at Harvard Medical School in Boston, says the evidence for overweight, obesity, and physical inactivity contributing to cancer is now “sufficiently strong to support strong actions to reduce these hazards.”

“Multiple and increasingly intensive strategies will be needed to reverse the obesity epidemic, and actions are needed in many sectors and at all levels of society,” he writes.

Dr. Willet comments that research on diet and cancer is “extremely challenging,” and the evidence has usually been published piecemeal in scientific journals. A major achievement has been the demonstration of overweight and obesity as an established cause of many common cancers, he says. Physical inactivity is also now well established as a risk factor for several cancers, and consumption of red meat, particularly processed red meat, is related to moderately higher risks.

“Although the risks of cancer are for an individual who is overweight or obese are not as great as they are for a tobacco smoker, in the United States and some other countries, the much higher prevalence of overweight and obesity than smoking means that the numbers of cancer deaths caused by these 2 factors are now similar,” he comments.

“Control of overweight and obesity must be a high priority for cancer prevention,” Dr. Willet comments. These efforts should be closely integrated with those for the prevention of other diseases, such as cardiovascular disease and type 2 diabetes, he adds.

Although the dietary factors related to obesity are complex, sugar-sweetened beverages such as soda have emerged as a particularly important contributing factor in many places, he adds. Increasing taxation/prices has a clear effect on decreasing soda consumption. “The scientific evidence base to support soda taxation has become much more solid in the past several years, and this should be pursued vigorously as a public health strategy,” he comments.

“In the United States, political gridlock and the powerful influences of the food and beverage industries often make national actions impossible,” he comments. Progress is frequently easier on a city or state level, he adds, noting that soda is now banned at many schools, and Boston (where he is based) does not allow the sale of soda on any city property.

Some progress has been documented, he says, citing a study that he was involved with that found a decline in the consumption of sugar-sweetened beverages in recent years in the United States (N Engl J Med. 2009;361:1599-1605).

“We have now begun to see some evidence of success, but sustained efforts will be needed for many years,” Dr. Willet concludes.

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