As the global cost of treatment skyrockets, measures to prevent people getting cancer in the first place are increasingly important in seeking to limit the expected explosion.
"The way things will evolve over, let's say the next 20 years, are very dramatic; many countries (will have) probably twice as many cancers," said Christopher Wild, Director, WHO's International Agency for Research on Cancer (IARC).
"That's particularly true for countries with limited resources, the low and middle-income countries," he told AFP.
With less access to diagnosis and treatment, these countries already bear two-thirds of the world's annual 8.8 million cancer deaths. In 2015, governments and patients spent an estimated $107 billion (99 billion euros) on cancer drugs -- an increase of 11.5 percent from 2014, according to the Global Oncology Trend Report of the IMS Institute. The figure was expected to grow to $150 billion by 2020, it said, a rise driven largely by the expense of newer, more specialised drugs to which just a minority of patients have access.
"Treating our way out of the cancer problem is not realistic," Wild told AFP on the eve of Saturday's World Cancer Day.
According to the WHO, with prevention, on the other hand, as much as a third of cancers can be avoided today. Public enemy number one is tobacco, which "will kill a billion people in the world in the 21st century," said Thierry Philip, president of the Institut Curie cancer research centre in Paris.
The known causes
Of these, 100 million will be in China alone.
Cervical cancer, in turn, can be avoided by vaccinating against the human papilloma virus (HPV). Regular screening can pick up pre-cancerous lesions, which can be treated before developing into full-blown disease. Physical inactivity, obesity and heavy drinking are risks factors for all sorts of cancer, while eating too much red and preserved meat can lead to cancer of the colon, says the WHO.
Too much sun, easily avoided by wearing a hat or seeking out the shade, causes melanoma. Vaccination prevents Hepatitis B infection, which can lead to cancer, and basic, good hygiene can thwart the bacterium Helicobacter Pylori, which boosts the risk of stomach cancer.
"We already know a lot about the causes of cancer," said Wild. We could probably prevent 40 to 50 percent of cancers if we could really convert our knowledge about risk factors into effective interventions."
But while investment in new treatments has exploded, prevention "has certainly been under-resourced," he added. Part of the reason is commercial -- the pharma industry stands to make little money from research into preventing disease.
For prevention, "the return on investment only comes after 10, 20, 30 years, which is hard to defend in a tough economic environment," said Beatrice Fervers of the Centre Leon-Berard, a research clinic in Lyon, France.
According to the WHO, cancer care and labour productivity lost to illness and death cost the world about $1.16 trillion in 2010.
Not too strict
"One of the things we have to change is to stop thinking about cancer prevention only as an individual responsibility," said Wild.
"It's also government responsibility, it's about policies and legislation," he said -- citing tobacco taxes.
Other interventions should include vastly expanding HPV and Hepatitis vaccination, cleaning up polluted air and water, and regularly checking people with a genetic predisposition for certain cancers. Furthermore, people should be better educated about lifestyle choices that put them at risk.
"We need to translate the science for the public, make it accessible and warn people of the real risk between cancer and behaviour," said Fervers.
"The risk, if there are too many recommendations, too many constraints, people will just throw it all overboard," she added -- like advising French people to steer clear of wine.
"We need to adapt the message to the context, to the culture," said Servers. "If we can get people to respect a limit of one or two units (of alcohol) per day, that would already be something."
On Friday, the WHO unveiled new global guidelines with an aim to place more emphasis on early cancer diagnosis and treatment.
"Too many cancers arrive too late in the health system," Etienne Krug, head of the UN health body's noncommunicable diseases division, said in Geneva, adding, "millions of lives could be saved."
The guidelines urge countries to improve awareness of cancer symptoms and encourage people to seek care.