Why did we create the Cancer FactFinder?

Most everyone has had some kind of personal experience with cancer, and many of us worry about what causes it. So it’s not surprising that cancer is one of the most researched topics online.

We often turn to social media, internet searches, and friends or family for information about cancer. All of these can give us a wealth of information to help make decisions about lifestyle, nutrition, and health and to help avoid a cancer diagnosis. But this requires having accurate information.

It is often difficult to know which information is reliable—meaning which information can and cannot be trusted about what does, and what does not, cause cancer. We created this site to give people ready access to accurate information about cancer so they can make informed choices to avoid certain exposures or to take positive steps to maximize
their health.

How do we gather and process information for the FactFinder?

We review summaries of evidence in a manner consistent with other major organizations and share what we know about how strong the evidence is and whether something is or is not associated with cancer. To do this, we use the following systematic and stringent process to identify claims about cancer causes in studies of humans:

We search for cancer claims from the internet, social media, and other sources.

Once identified, our editorial staff verify or refute these claims using the best available studies in humans and laboratory/supporting studies. We go to reliable sources of scientific data, including medical and scientific journals, obtain expert opinions by leading scientists, and abstract information from reputable organizations such as the American Cancer Society and the National Institutes of Health.

 To decide whether a claim is likely true or false, we limit our review to evidence that provides information on strength of association or causation. This means that the criteria we use to make our conclusions include information about exposures and factors that are known to cause cancer. However, causation can’t always be established. We also consider the evidence for reliable associations with cancer in humans based on epidemiological evidence. We also evaluate findings from toxicology studies and other supporting studies, in addition to the current epidemiological evidence.

 We also base our conclusions about cancer causes primarily on epidemiological studies done in humans. Experimental studies, including animal and laboratory investigations, can provide supportive information, but ultimately, human epidemiological evidence was used to determine cancer risk.

 Note that not all associations with cancer can be found by epidemiological studies, so there are still unknowns about some claims of cancer causes, especially when it involves something that may or is known to contain cancer-causing agents (carcinogens). Laboratory studies and supporting evidence are also limited since the subjects of study are not humans. While these conclusions may show an effect in animals, it cannot always be applied to humans since the subjects are different. These limitations are noted in individual claim descriptions. 

 We then summarize the information we have and discuss it with our editorial team.

 After a summary of the information is drafted, editors with specialized expertise edit and fact-check the written summary.

We share this summary with members of the community, including cancer survivors and advocates, to ensure the message is clear and addresses the points that may be of concern to the general readership—not just the experts in a field.

Once fully vetted, we share the information through this FactFinder site so that it is available to the general public.

Note: Be aware that some exposures or risk factors that may not cause cancer could have other health effects, either harmful or beneficial. We do not provide information on this site about other effects that may be relevant to health outside of cancer.

What information is not included in our summaries?

Experimental studies, including animal and laboratory investigations, can provide valuable information. We didn’t consider evidence from animal and laboratory studies here, even though regulators routinely use this type of experimental evidence to evaluate chemicals for safety in the U.S. and the European Union.

Since we did not include animal studies in our report, we may have missed some important information about factors that cause cancer. Because it is unethical to expose humans to a risky chemical in a study, animal and laboratory studies are the only way to determine whether some exposures cause cancer. Figuring out the causes of cancer can require putting together information from many other sources, including observations when humans have been exposed through their everyday life, at work, or in accidents, and considering evidence from experiments in animals or cells. Evidence from cancer studies in humans often emerges only after people have been exposed for decades.