Page 12 Complete Your CE Test Online - Click Here individuals are exposed occasionally, and might be unable to recall the exposure, even if they knew about it when it happened. Some people wonder how many cancers are caused by involuntary (and possibly unknown) exposure to carcinogens in the environment. But this question cannot be answered with certainty. Some researchers have suggested that, in most populations, environmental exposures are responsible for a relatively small proportion of total cancers (less than 4%), whereas other researchers attribute a higher proportion (19%) to environmental exposures. Of course, as health professionals we know that even ongoing exposure to carcinogens does not cause cancer in every person. Incidental or brief exposure, even to most of the known carcinogens, is not likely to significantly raise cancer risk because risk is typically dose related. We also know that there are specific routes of exposure that are most likely to cause problems, routes the carcinogen is absorbed into the body and the type or types of cancer it can cause. For instance, daily exposure to cigarette smoke by deliberate inhalation is clearly much more likely to produce cancer than occasional exposure to smoke from a wood fire. People who work with carcinogens every day and do not wash up or use protective equipment are more likely to develop cancer than the hobbyist who is exposed only every few months. Painful questions about a loved one’s cancer can mean that patients and families read online stories and theories that arouse fears about everyday exposures. Those who do not have cancer (or those who have completed treatment) often want to know how to avoid all possible carcinogenic exposures in the future to further protect their health. There is a lot of easy-to-find information online that may seem plausible to the layperson even though it has no scientific basis at all. Other online sources raise questions and voice concerns but do not have much to go on. This is why nurses need to be able to find proven, up-to-date information. Organizations with evidence-based information on cancer and carcinogens A great deal of reliable data for health care professionals can be found online. The National Cancer Institute has recommendations on where to look for source information. Since 1971, the International Agency for Research on Cancer (IARC) has evaluated all manner of studies on more than 900 agents, including chemicals, complex mixtures, occupational exposures, physical agents, biological agents, and lifestyle factors. Of these, more than 400 have been identified as carcinogenic, probably carcinogenic, or possibly carcinogenic to humans. The IARC also keeps files on those that are not considered to be carcinogenic, which can be quite helpful in eliminating possible risk factors. The U.S. National Toxicology Program (NTP) has classified 56 substances or exposures as carcinogenic and nearly 200 more as “reasonably anticipated to be human carcinogens.” The American Cancer Society also has a special Known and Probable Human Carcinogens list pooled from both of these reliable sources and listed on a single web page ( along with background information about carcinogens. But to find specifics about a suspect carcinogen (study summaries, routes of exposure), professionals will still want to see the more detailed reports on the substance or exposure on the IARC or NTP website. Evidence-Based Practice: Find reliable, well-researched information and full background research reports about known and suspected carcinogens online at the U.S. National Toxicology Program (NTP) and the International Agency for Research on Cancer (IARC) at and http:// For substances that cannot be found listed as carcinogens on either of these lists, the first step is to look for other names for the substance. Sometimes the chemical name listed in the reports is not exactly the same one found in other sources. Search engines can often help find information on reliable science websites that list multiple synonyms and common names for chemicals. Having a list like this can help find research-based information for patients with possible carcinogen exposure or help them to find information for themselves. The U.S. National Cancer Institute (NCI) has information about what causes cancer. See prevention/risk/substances/carcinogens. The NCI has links to the specialty groups the U.S. National Toxicology Program (NTP) and the International Agency for Research on Cancer (IARC), which is part of the World Health Organization. There is also access to good research in websites like PubMed, (see section “Resources for Nurses” or “Disproven Carcinogens and Other Cancer Myths”). Risk Factors Age Advancing age is the most important risk factor for cancer overall and for many individual cancer types (Figure 1). According to the most recent statistical data, the median age of a cancer diagnosis is 66 years. This means that half of cancer cases occur in people below this age and half in people above this age. One-quarter of new cancer cases are diagnosed in people aged 65 to 74. A similar pattern is seen for many common types of cancer. For example, the median age at diagnosis is 61 years for breast cancer, 68 years for colorectal cancer, 70 years for lung cancer, and 66 years for prostate cancer. Figure 1. Percent of New Cancers by Age Group: All Cancer Sites. SEER 18 2007-2011, adapted from NCI. All Races, Both Sexes.