Page 29 Complete Your CE Test Online - Click Here and may even initiate these types of cancers. Tanning beds put out large amounts of UV-A radiation [257]. UV-A can pass through most windows (depending on type of glass), and is not affected by altitude or weather [300]. UV-B rays are harmful, and are known to cause sunburn. Exposure to UV-B rays increases the risk of DNA damage and other cellular damage in all living organisms, not just humans. Fortunately, about 95% of UV-B rays are absorbed by the ozone in the Earth’s atmosphere [136]. But the remaining percentage leaves plenty of cancer-causing UV rays to be absorbed by human skin [257]. UV-B rays are most intense from mid-spring through mid-fall in the U.S., and during the daytime between 10a.m. and 4p.m.; however, UV-B rays can damage skin, or even burn it, year-round. This happens more in the southernmost parts of the U.S., at high altitudes, and on surfaces that reflect back sunlight, e.g. water, sand, snow, or ice [136]. UV-B rays are also associated with cataracts, but help the body make vitamin D, a necessary vitamin. UV-B rays do not significantly penetrate windows [300]. Intermittent versus cumulative UV exposure Most evidence about UV radiation exposure and the prevention of skin cancer comes from observational and analytical studies. Such studies have consistently shown that increased cumulative sun exposure is a risk factor for non-melanoma skin cancers, such as basal and squamous cell cancers [86,243]. Exposure to solar UV radiation is the major cause of non-melanoma skin cancers, which are by far the most common malignancies in humans [147]. But the relationship between UV radiation exposure and cutaneous melanoma is less clear than that of non-melanoma skin cancers. In the case of melanoma, it seems that intermittent acute sun exposure leading to serious sunburn is more important than cumulative sun exposure [93]. Sunburn sustained during childhood or adolescence may be particularly important [113]. And it is also important to know that acral lentiginous melanoma, a very aggressive form of melanoma that usually forms in areas not often exposed to sunlight such as mucous membranes, the palms, soles of the feet or under nails, is much more common among darker-skinned people [256]. Immunosuppression Medications that suppress the immune system are associated with an increased cancer risk. Many people who receive organ transplants take immunosuppressant drugs to ensure the body will not “reject” the organ. These medications make the immune system less able to detect and destroy cancer cells or fight off infections that cause cancer [85,148]. Research has shown that transplant recipients are at increased risk of a large number of different cancers. Some of these cancers can be caused by infectious agents, whereas others are not. The four cancers which occur more commonly in transplant recipients than in the general population are non-Hodgkin’s lymphoma (NHL) and cancers of the lung, kidney, and liver. NHL can be caused by Epstein-Barr virus (EBV) infection, and liver cancer by chronic infection with the hepatitis B (HBV) and hepatitis C (HCV) viruses. Lung and kidney cancers are not generally thought to be associated with infection [170]. Infection with HIV weakens the immune system and increases the risk of certain cancers, especially those that are caused by infections (see section “Infectious Agents”). HIV infection is also linked to increased risks of cancers that are not thought to be caused by infectious agents, such as lung cancer [170]. Other carcinogens Any substance that is known to be able to cause cancer is classified as a carcinogen, but carcinogenesis is rarely simple. Many factors influence whether a person exposed to a carcinogen will develop cancer, including the amount, duration, and route of exposure as well as the person’s age, and genetic background. Cancers caused by involuntary exposures to environmental carcinogens are most likely to be seen in subgroups of the population, such as workers in certain industries who may be exposed to carcinogens on the job [161]. In fact, that is the way a lot of causal links have been found– workers who are exposed to a carcinogenic substance every workday for years are often the first ones found to have higher rates of a certain type of cancer, which often leads to a formal investigation of the substances to which they are exposed. The increased incidence in a small exposed group is much easier to detect and demonstrate than when scattered individuals are exposed occasionally, and might be unable to recall the exposure, even if s/he knew about it when it happened [56]. 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 four percent), whereas other researchers attribute a higher proportion (19 percent) to environmental exposures [161]. 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, i.e. 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 only exposed 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 healthcare professionals can be found online. The National Cancer Institute has recommendations on where to look for source information [161]: ● ● 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