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How Much Cancer Might Be Prevented?

In February 2014, an International Agency for Research on Cancer (IARC)/World Health Organization (WHO) headline proclaimed:

Global battle against cancer won’t be won with treatment alone. Effective prevention measures urgently needed to prevent cancer crisis.

The WHO states:

Prevention offers the most cost-effective long-term strategy for the control of cancer.

Whenever cancer incidence rates have fallen, prevention was key — reducing cancer-causing exposures at work, home, school or play, healthier diets and active lifestyles. Estimates of how much cancer can be prevented range from 30%, up to 95% or more for some tumours.

Wherever cancer rates have fallen, prevention was key.

The 2010 US President’s Cancer Report Reducing Environmental Cancer Risk, What We Can Do Now found that, “the true burden of environmentally induced cancer has been grossly underestimated.”

The American Institute for Cancer Research states that a third or more cancers (depending upon the type of cancer) can be prevented with exercise, good diet, maintaining a healthy weight, and not smoking.

The World Health Organization echoes this, recommending to avoid environmental and occupational carcinogens, and infections that lead to cancers.

The Canadian Cancer Society says that half of cancers can be prevented through lifestyle changes. They also say that 5% to 10% of cancers are related to inherited genetic abnormalities, which suggests that 90% to 95% of cancers could be preventable.

Even genetic pre-dispositions are not a death sentence. Dr. Judith Stern of the University of California famously said:

The Canadian Cancer Society says that half of cancers can be prevented through lifestyle changes.

“The genes load the gun, but the environment pulls the trigger.”

In this context, George Church of Harvard Medical School commented that the genetics conversation has evolved from “Here is your destiny, get used to it,” to:

“Here is your destiny, and you can do something about it!”

“Doing something about it” lies in choices we make for ourselves such as exercising, eating healthy food, and not smoking or vaping.

We have less power over many factors, affecting our air, water, food and surroundings — the environment.

Our chances of developing cancer can be affected by where we live. Community amenities (e.g., access to healthy food and recreation), occupational and shared exposures from industries, and exposures from infrastructure such as pollution from busy roads and increasing numbers and power of wireless antennas (outdoors and indoors), are some factors that may affect likelihood of cancers in communities.

Counting Cancer:
What statisticians report

The number or fraction of people who are diagnosed per year.

The number or fraction of people with the disease at any given time.

The number or fraction of people who die of the condition per year.

Years of Life Lost:
The difference between age at death, and normal life-span.

Older people are more likely to develop cancer, so statistics are usually adjusted to a standard age profile.

If treatment improves and people live with the condition for longer, prevalence goes up. Mortality would decrease at least temporarily, or may fall permanently if affected individuals die of other causes.

For those interested in prevention, incidence is the most important statistic, which was available in 2001 (Figure 1). In 2014, the Public Health Agency of Canada only mapped prevalence (Figure 2).

Fine-grained data used to be available through the Public Health Agency of Canada (on the left). Historical data indicates large disparities in incidence in 2001, and in prevalence in 2014.

[could make a couple of graphs from here – Centre for Surveillance and Applied Research, Public Health Agency of Canada. Canadian Cancer Data Tool (CCDT), 2021 Edition. Public Health Infobase. Ottawa (ON): Public Health Agency of Canada, 2021.]

The bottom line is that every day we are exposed to numerous contributors to cancer, and these can build on effects of yesterday’s, last year’s and childhood exposures. Even exposures before birth, and of mothers and grandmothers can influence offsprings’ development. For example, grandmothers’ exposure to the endocrine-disrupting, carcinogenic insecticide DDT causes earlier menstruation and more obesity (conditions that are linked to higher risk of breast cancer) in granddaughters. DDT was eventually banned in Canada, the US and Europe, but it is still used in some countries for mosquito control.

Profound humility with what remains unknown, must lead us to opt for least-toxic approaches.