Page 47 Complete Your CE Test Online - Click Here Breast cancer risk reduction for women at high risk Women known to have significantly increased breast cancer risk can use chemoprevention in the form of tamoxifen (for premenopausal women) or raloxifene (for postmenopausal women), which have both been FDA approved for this purpose. Studies show an overall relative risk reduction of about 38% for this preventive measure. This means that woman with an 8% risk of breast cancer in the next five years (which is pretty high) would see their absolute risk cut to about 5% with this drug treatment. But healthy women at age 60 would have about a 1.7% chance of breast cancer over the next five years, and a 38% risk reduction would drop their absolute risk to about 1.05%. The absolute benefit is clearly much less for women at average risk of breast cancer. Tamoxifen decreased only estrogen receptor-positive cancer and DCIS, but the effect lasted for 16 years after starting tamoxifen (11 years after finishing the five-year course). These drugs also have risks, which is another reason they are not recommended for general use in breast cancer prevention. Tamoxifen can cause symptoms of menopause and slightly increase the risk of cancer of the uterus, and both drugs can rarely cause blood clots (DVT or pulmonary embolus). Women who are pregnant, breastfeeding, at high risk of blood clots, or taking estrogen should not take either drug for breast cancer prevention. Women who smoke or are obese, hypertensive, or diabetic are at increased risk of blood clots. Tamoxifen should not be used in women who have had uterine cancer or precancerous lesions (atypical hyperplasia) of the uterus. Aromatase inhibitors have shown that they can also reduce breast cancer risk in postmenopausal women at increased breast cancer risk, but have not been approved for that purpose as of 2016. Prophylactic bilateral mastectomy can also reduce risk in women with strong family histories of breast cancer. Premenopausal women with BRCA gene mutations who undergo prophylactic oophorectomy have lower breast cancer incidence. Oophorectomy, or ovarian ablation, is linked to decreased breast cancer incidence in normal premenopausal women and in women with increased breast cancer risk resulting from thoracic irradiation. Carcinogen exposure People are generally interested in reducing their exposure to carcinogenic substances whenever possible. In fact, the state of California passed a law (Proposition 65, also called the Safe Drinking Water and Toxic Enforcement Act of 1986) that set up its own registry and labeling requirements for products that contain or possibly contain carcinogens or that might cause reproductive toxicity. Unfortunately, the labels do not say what or how much is in the product or the likelihood of exposure with normal use, so it is not especially helpful to most people who want to make judicious decisions about exposure (unless they have enough time to contact each manufacturer, learn what is in the product, and then find information on the target substance). Workplace exposures Regulations have been put in place in the U.S. to reduce exposures to known carcinogens in the workplace and to allow workers to find out about substances at work that may be carcinogenic or toxic in other ways. (See Table 6.) Table 6. Cancers associated with various occupations or occupational exposure Cancer Substances or processes Lung Arsenic, asbestos, cadmium, coke oven fumes, chromium compounds, coal gasification, nickel refining, foundry substances, radon, soot, tars, oils, silica. Bladder Aluminum production, rubber industry, leather industry, 4-aminobiphenyl, benzidine. Nasal cavity and sinuses Formaldehyde, isopropyl alcohol manufacture, mustard gas, nickel refining, leather dust, wood dust. Larynx Asbestos, isopropyl alcohol, mustard gas. Pharynx Formaldehyde, mustard gas. Mesothelioma Asbestos. Lymphatic and hematopoietic Benzene, ethylene oxide, herbicides, X-radiation system. Skin Arsenic, coal tars, mineral oils, sunlight. Soft tissue sarcoma Chlorophenols, chlorophenoxy herbicides. Liver Arsenic, vinyl chloride. Lip Sunlight. Adapted from Agency for Toxic Substances and Disease Registry, CDC: Chemicals, Cancer, and You (2009) Outside of the workplace, most people can take steps to limit their exposure to known carcinogens: ● ● Testing basements for radon. ● ● Avoiding tobacco smoke and tobacco use. ● ● Reading labels before using chemicals and substances (e.g., some common insecticides and herbicides were upgraded in 2015 to “possibly” or “probably” carcinogenic in humans by the IARC 0). ● ● Limiting UV exposure. ● ● Maintaining a healthy weight. ● ● Limiting alcohol intake. Dietary and exercise recommendations for cancer prevention The National Cancer Institute reports that the evidence for influence of dietary factors and cancer is uncertain. There is difficulty evaluating the impact of diet on cancer risk because although lifelong dietary patterns or dietary intake during specific life stages may be important in cancer development, they are not likely detected by relatively short-term randomized clinical trials. Attempts to quantify the role of diet have been based on systematic reviews of epidemiologic evidence, which found that the greatest consistency was seen for nonstarchy vegetables and fruits. These were linked to probable decreased risk for upper GI cancers. Fruits were also linked to a probable decreased risk for lung cancer. In relation to human cancer, diets reflect the sum total of a complex mixture of exposures. No dietary factors appear to be uniformly relevant to all forms of cancer. Nevertheless, the American Cancer Society has specific dietary and physical activity recommendations. The following are adapted from American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention: 1. Maintain a healthy weight. ○ ○ Stay lean without being underweight. ○ ○ Avoid excess weight gain. If currently overweight or obese, start by losing small amounts. ○ ○ Use regular exercise and limit high-calorie foods to reach or maintain a healthy weight. 2. Cultivate physically active habits. ○ ○ Each week, adults should exercise at least 150 minutes at moderate intensity or 75 minutes at vigorous intensity or equivalent, spread throughout the week if possible. ○ ○ Teens and children should exercise at least one hour (moderate or vigorous intensity) each day, with vigorous intensity on at least three days of the week. ○ ○ Limit time spend sitting, reclining, and watching TV and other electronic screens. 3. Eat a healthy diet that emphasizes plant foods. ○ ○ Limit intake of processed meats (e.g., bacon, bologna, sausage, luncheon meats, hot dogs, cured meats) and red meats (e.g., beef, pork, lamb). ○ ○ Eat five servings (about 2.5 cups total) of a variety of vegetables and fruits every day.