Chapter 078. Prevention and Early Detection of Cancer (Part 2)

Physical Activity Physical activity is associated with a decreased risk of colon and breast cancer. A variety of mechanisms have been proposed. However, such studies are prone to confounding factors such as recall bias, association of exercise with other health-related practices, and effects of preclinical cancers on exercise habits (reverse causality). Recommending adults to engage in at least 30 min of vigorous activity for ≥3 days a week is good health advice, though its effects on cancer incidence are unproven.Diet ModificationInternational epidemiologic studies suggest that diets high in fat are associated with increased risk for cancers of the breast,...
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Chapter 078. Prevention and Early Detection of Cancer (Part 2) Chapter 078. Prevention and Early Detection of Cancer (Part 2) Physical Activity Physical activity is associated with a decreased risk of colon and breastcancer. A variety of mechanisms have been proposed. However, such studies areprone to confounding factors such as recall bias, association of exercise with otherhealth-related practices, and effects of preclinical cancers on exercise habits(reverse causality). Recommending adults to engage in at least 30 min of vigorousactivity for ≥3 days a week is good health advice, though its effects on cancerincidence are unproven. Diet Modification International epidemiologic studies suggest that diets high in fat areassociated with increased risk for cancers of the breast, colon, prostate, andendometrium. These cancers have their highest incidence and mortalities inwestern culture where fat comprises an average of 40–45% of the total caloriesconsumed. In populations at low risk for these cancers, fat accounts for Fiber binds oxidized bile acids and generates soluble fiber products, such asbutyrate, that may have differentiating properties. Fiber does not increase boweltransit times. High-fiber diets could lower the risk of breast and prostate cancer byabsorbing and inactivating dietary estrogenic and androgenic cancer promoters.However, two large prospective cohort studies of >100,000 health professionalsshowed no association between fruit and vegetable intake and risk of cancer. The Polyp Prevention Trial randomly assigned 2000 elderly persons, whohad polyps removed, to a low-fat, high-fiber diet versus routine diet for 4 years.No differences were noted in polyp formation. The U.S. National Institutes of Health Womens Health Initiative, launchedin 1994, is a long-term clinical trial enrolling >100,000 women aged 45–69. Itplaced women in 22 intervention groups. Participants received calcium/vitamin Dsupplementation, hormone-replacement therapy, and counseling to increaseexercise, eat a low-fat diet, and cease smoking. The study showed that whiledietary fat intake was significantly lower in the diet intervention group, invasivebreast cancers were not reduced over an 8-year follow-up period compared to thecontrol group. The difference in dietary fat averaged ~10% between the twogroups. Scientific evidence does not currently establish the anticarcinogenic valueof vitamin, mineral, or nutritional supplements in amounts greater than thoseprovided by a balanced diet. However, consuming at least five servings of fruitsand vegetables a day decreases dietary fat and increases fiber; such a diet maylower the risk of cardiovascular disease even if it does not influence cancer. Energy Balance Risk of cancer increases as body mass index increases over 25 kg/m2.Obesity increases risks for cancers of the colon, breast (female postmenopausal),endometrium, kidney (renal cell), and esophagus, although causality is notestablished. Relative risks of colon cancer are increased in obesity by 1.5–2.0 for menand 1.2–1.5 for women. Obese postmenopausal women have a 30–50% increasedrisk of breast cancer. A hypothesis for the association is that adipose tissue servesas a depot for aromatase that facilitates estrogen production. Adiposity is alsoassociated with poorer survival and increased risk of recurrence after treatment. Sun Avoidance Nonmelanoma skin cancers (basal cell and squamous cell) are induced bycumulative exposure to ultraviolet (UV) radiation. Intermittent acute sun exposureand sun damage have been linked to melanoma. Sunburns, especially in childhoodand adolescence, are associated with increased risk of melanoma in adulthood.Reduction of sun exposure through use of protective clothing and changingpatterns of outdoor activities can reduce skin cancer risk. Sunscreens decrease therisk of actinic keratoses, the precursor to squamous cell skin cancer, but melanomarisk may be increased. Sunscreens prevent burning, but they may encourage moreprolonged exposure to the sun and may not filter out wavelengths of energy thatcause melanoma. Educational interventions to help individuals accurately assess their risk ofdeveloping skin cancer have some impact. Self examination for skin pigmentcharacteristics associated with melanoma, such as freckling, may be useful inidentifying people at high risk. Those who recognize themselves as being at risktend to be more compliant with sun-avoidance recommendations. Risk factors formelanoma include a propensity to sunburn, a large number of benign melanocyticnevi, and atypical nevi.