Page 22 Complete Your CE Test Online - Click Here search for the primary cancer may involve lab tests, X-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI) scans, positron emission tomography (PET) scans, and other procedures. However, in some patients, a metastatic tumor is diagnosed but the primary tumor cannot be found despite extensive tests. The pathologist knows that the diagnosed tumor is a metastasis because the cells do not look like those of the organ or tissue in which the tumor was found. Doctors refer to the primary cancer as unknown or occult and the patient is said to have cancer of unknown primary (CUP). Because diagnostic techniques are constantly improving, the incidence of CUP is decreasing [176]. While CUP can be treated with a number of cancer treatments, cure is generally unlikely because the cancer typically has multiple metastatic sites. WHAT CAUSES CANCER? Cancer can be caused or promoted by external exposures or events, such as smoking, ultraviolet radiation, and medications that suppress the immune system. Cancer can also be caused by other health conditions or problems, including: inherited and acquired genetic mutations; the internal hormonal environment; and poor immune function. These kinds of exposures and conditions can act synergistically and/or in sequence to initiate and promote cancer growth. When there is exposure to a carcinogenic event or substance, it is common for ten or more years to elapse between the exposure and the cancer diagnosis, although it is often much longer than a decade (see section, “Cancer Risks and Carcinogens”). This latency period varies by type of exposure and type of cancer as well as other factors [14]. It is very difficult in a given cancer case to pinpoint any one cause. More commonly, health care professionals can only point to a group of risk factors as the most likely to have affected the patient’s development of cancer. Sometimes, there are few known risk factors for a person’s cancer beyond older age and sex. Information from the Internet or other sources can be unreliable When patients and families want to know about cancer and links to causality, they often do not know where to look for reliable information. There are so many unfounded theories posing as facts on the internet and social media. Health care professionals can look at reliable sources such as PubMed to find out whether or not an actual peer-reviewed study has been published and what kind of link is postulated (see section, “Resources for Nurses”). A lot of the information easily found online does not have any kind of reliable study associated. Although a site or post may refer to “research” or “studies,” it is often the case that no citations are given. Unfortunately, even if there are studies, most research does not examine causality; many widely-publicized studies are strictly observational. If a study is only researching correlations, it might report, for instance, that weight loss is correlated with cancer, or with death. This would certainly sound familiar to nurses, because most people lose weight when they have cancer or another serious illness. However, this is statistically termed confounding. Incredulously, some study reports confuse things like this, in this case implying that poor nutrition was the cause of the illness and death. Illness caused the weight loss and not the other way around. Although this may seem like a silly example, non-medical writers often do not understand such obvious issues as reverse causality or confounding. And even statisticians do not always know about basic anatomical processes, e.g. cachexia of chronic disease. Cancer risk factors and carcinogens Cancer risk factors include exposure to chemicals or other substances, as well as certain behaviors. They include things people cannot control, like age and family history. Other risks can be controlled. Likewise, some carcinogens can be avoided, but others cannot. Limiting exposure to avoidable risk factors may lower the risk of developing certain cancers [176]. Lifestyle, diet, and exercise Obesity People who are obese may have an increased risk of several types of cancer, including cancers of the breast (in women who have been through menopause), colon, rectum, endometrium, esophagus, kidney, pancreas, and gallbladder [180]. Conversely, eating a healthy diet, being physically active, and maintaining a healthy weight may help reduce risk of some cancers [115]. These healthy behaviors also help to lessen the risk of some other illnesses, such as heart disease, Type-II diabetes, and high blood pressure (see section “Cancer Prevention”). Tobacco Decades of research have consistently established a strong causal link between tobacco use and cancers. Smoking is associated with one out of every three cancer deaths (32%), and four out of every five lung cancer deaths (80%) [14]. Cardiovascular disease, heart attacks, strokes, COPD, ectopic pregnancy, erectile dysfunction, and gingivitis are other health risks that are elevated for tobacco users [27]. Cigarette smoking: According to the National Cancer Institute (NCI), cigarette smoking is strongly correlated with the following cancers or cancer sites [70, 156, 233]: ● ● Lung. ● ● Oral cavity. ● ● Pharynx. ● ● Larynx. ● ● Esophagus. ● ● Bladder. ● ● Kidney. ● ● Pancreas. ● ● Stomach. ● ● Cervix. ● ● Acute myelogenous leukemia. The NCI notes that the body of evidence confirming these links is substantial. Further support is demonstrated by the lung cancer death rates in the U.S., which have mirrored smoking patterns [148]. The risks of lung cancer due to smoking are dose-dependent and increase markedly by the number of years smoked; cancer and other health risks also increase with number of cigarettes smoked per day [174]. Some of the risk increase relates to the smoker’s age: in the general population (which includes both smokers and nonsmokers) the average probability of a man developing lung cancer goes from one in 608 from to age 49, to one in 16 when the man is 70 or older [14]. Current smokers, on average, have about 20 times the risk of lung cancer compared to nonsmokers [174]. It is easy to see that young smokers who just started smoking are at much less immediate risk than someone who is older and has smoked 30 years. Daily smoking means constant exposure to harmful chemicals. Of the more than 7,000 chemicals in tobacco smoke, at least 250 are known to be harmful, including hydrogen cyanide, carbon monoxide, and ammonia. Among the 250 known harmful chemicals in tobacco