A recent report highlighted the progress made globally in preventing cancer. However, improvements are still needed.
A staggering 2/5 of all cancers diagnosed around the globe are considered to be avoidable, according to the third edition of the Cancer Atlas.
Tobacco use, infectious agents, unhealthy diet, excess body weight, physical inactivity, and alcohol consumption accounted for the majority of risk factors associated with cancer death, according to the report, which was produced by the American Cancer Society (ACS), the Union for International Cancer Control (UICC), and the International Agency for Research on Cancer (IARC).
But while doctors and health agencies worldwide hope to stave off behaviors associated with these risks, there could be a big global shift in the cancer burden coming in the 21st century. Tobacco use is down in the United States and other developed countries, who are also expected to curb infection-caused cancers-like cervical cancers caused by human papillomavirus (HPV), according to the report. At the same time, those countries could see an increase in lifestyle-driven cancers because of diet and obesity, as well as increased tobacco use.
Societal and behavioral changes mean that some things will change regionally; however, these could then affect another region afterward, said Lindsey Torre, MSPH, an epidemiologist at ACS, in a recent interview with CancerNetwork®.
“It depends what country we’re talking about,” she added. “The major contributor, of course, is tobacco smoking-and that accounts for so many of these potentially avoidable cancers, so we could see the proportion of preventable cancers decline… But you’ve got this mix of other factors.”
In places like the United States, lung cancer remains almost as deadly as it was decades ago. The 5-year-survival rate among those with lung cancer has climbed from 12% to 21% since the 1970s, while other tumor types have seen much more dramatic improvements, said Torre.
However, dramatically plummeting smoking rates have pushed incidence of the disease down. One telling statistic was the fact that American high schoolers’ cigarette use dropped by half from 2011 to 2018 (about 16% to 8%), according to the report.
Unforunately, the report also found that developing countries have increased their smoking habits, which will, in turn, increase cancer incidence rates globally. For instance, an estimated 2.3 million cancer deaths, or about a quarter of the death toll, was counted in 2017. This burden is increasingly coming from outside North America and Europe: 80% of the world’s smokers now live in low- and middle-income countries-and the world’s total smoker population is 1.1 billion, according to the Cancer Atlas.
Therefore, preventing individuals from starting to smoke is crucial. “In a lot of developed countries, smoking is decreasing, though a little more gradually these days, but it’s still declining,” Torre said. “If we can continue to see that decline, we would see the proportion of these preventable cancers decline…(In a) lot of (developing) countries, you’re not seeing tobacco (use) skyrocket, thankfully.”
Lifestyle factors such as excess body weight, poor diet, intake of alcohol, and lack of exercise are all factors now associated with the development of cancer, which occur more frequently in wealthier countries.
Excess body weight or obesity is a risk factor for 13 different types of cancer, including breast, kidney, liver, uterus, and colon, among others, the report said. Alcohol drives development of 7 different types of cancer, including the pharynx, larynx, and esophagus, among other locations, the report added.
Obesity and excess body weight accounted for 3.6% of all new cancer cases in 2012, the Cancer Atlas estimated, while alcohol consumption comprised 4.6% of all cancer deaths in 2016.
“With excess body weight, I don’t think any country has really seen it peak and start to decline yet. Maybe some countries are plateauing,” said Torre. “There’s increasing alcohol use, pretty much around the world.”
Fifteen percent of all cancers diagnosed worldwide are caused by infections, which vary by region. For instance, 1/3 of all cancer cases in Sub-Saharan Africa are due to infections-predominantly due to HPV. Among some of those countries, like Zambia, Tanzania, and Zimbabwe, the rate of infection-caused cancers is more than 40%, driven predominantly by cervical cancer caused by the virus.
All these cases are considered “preventable,” because of the HPV vaccine currently available, and also because screening offers the possibility of removing pre-cancerous lesions before they become full-fledged disease, said Torre.
While the vaccine can be costly when millions of doses are required, there are currently humanitarian efforts underway to provide the inoculations for free, or at lower costs, she added.
Other “hot spots” of infection-driven cancers vary. The bacteria Helicobacter pylori, and the stomach cancer it causes, is a problem in China and parts of East Asia. Other places have rampant hepatitis B and hepatitis C, like sections of Asia and the Pacific Islands and North Africa.
Vaccination and improvements in hygiene can help these countries to improve outcomes-especially when it comes to the African HPV epidemic, Torre said.
A Global Shift
The current rate of infection-driven cancer is 4% of all the disease burden in some very high-income countries, according to the Cancer Atlas.
“In developing countries, you’d probably expect virtually everything to increase… with the exception of maybe infection, which are being controlled more,” said Torre.
“It’s an interesting question, to prognosticate how all those factors would balance out,” she added.
Jemal A, Torre L, Soerjomataram I, Bray F (Eds). The Cancer Atlas. Third Ed. Atlanta, GA: American Cancer Society, 2019. http://canceratlas.cancer.org.