Cancer is a leading cause of death. Certain types of cancer share some of the same lifestyle and socioeconomic status risk factors as type 2 diabetes and cardiovascular disease. These findings suggest that lifestyle modification, including appropriate diet and nutri- tion, regular physical activity, weight control, and smoking cessa- tion can help to prevent certain types of cancers.
Below is a summary of some of the risk factors for several prevalent types of cancer.
Lung Cancer
In 2000, there were 1.1 million lung cancer deaths worldwide (Whitrow, et al., 2003). Lung cancer incidence increased dramati- cally in the 20thcentury and continues to increase in the 21stcentury (Teixeira, et al., 2003; Bray, et al., 2004).
Smoking
Cigarette smoking is the leading cause of lung cancer, and the disease risks are proportional to the intensity and duration of smoking and individuals who quit smoking lower their risks of lung cancer compared to those who continue to smoke (Burns,
2003). In addition to smoking, a number of demographic, geo- graphic, environmental, nutritional, genetic, hormonal, and lifestyle factors may be linked to an increased risk of lung cancer (Teixeira, et al., 2003). However, Whitrow, et al. (2003) note that there is limited evidence of causation other than for smoking.
Gender, age, racial/ethnic, and socioeconomic status differ- ences in smoking habits have been reported (Teixeira, et al., 2003;
Bray, et al., 2004; Patel, et al., 2004). With regard to gender, lung cancer is the leading cause of cancer-related deaths in U.S. women and accounts for as many deaths as breast cancer and all gynecol- ogical cancers combined (Patel, et al., 2004). In other developed countries, especially in Europe, there is an increased incidence of lung cancer in women (Teixeira, et al., 2003).
Despite all of the public health campaigns and interventions, 25% of women in the U.S. continue to smoke. Tobacco advertising targets women, and teenage girls face social pressures to smoke and engage in other risky behaviors (Patel, et al., 2004). Women begin to smoke earlier than men and have more difficulty trying to quit.
Moreover, women may be more susceptible to carcinogens than men, with women having a 1.5 times higher risk of develop- ing lung cancer than men with the same smoking habits (Teixeira, et al., 2003). Research is showing that women have different risks for developing lung cancer when compared to men. Women’s increased susceptibility to the negative effects of tobacco may occur because of their higher levels of DNAadducts, reduced DNA repair ability, increased frequency of mutations in tumor suppressor genes, and hormonal variations (Rivera and Stover, 2004).
There are a variety of gender differences in lung cancer pres- entation. Compared to men, there isa larger percentage of adeno- carcinoma among women, a larger proportion of young women, and non-smoking women are more likely to be diagnosed with lung cancer (Rivera and Stover, 2004).
There are also age differences in the histological type of lung cancer, with young people having a higher prevalence of adeno- carcinoma than older people (Teixeira, et al., 2003). Age differences may reflect differences in the type of cigarettes smoked and other factors (Marugame, et al., 2004).
With regard to racial/ethnic factors, smoking prevalence has been found to be higher among African-Americans compared to
whites (Stellman, et al., 2003). African-Americans also have a higher risk for lung cancer compared to whites in the U.S.
(Schwartz and Swanson, 1997). Among younger persons, this racial/ethnic disparity is greater.
African-American/white differences in lung cancer risks may be due to African- American/white differences in smoking habits.
Stellman, et al. (2003), using a hospital-based case-control design, found that African-Americans and whites who had similar smoking habits had similar lung cancer risks, except for African- Americans who were very heavy smokers. The investigators suggest that modifying factors, such as cigarette type, diet, occu- pation, and the variations in the ability to metabolize smoke car- cinogens may influence African-American/white differences in lung cancer risks.
Based on a survey of 5,588 cases of African-Americans and whites with lung cancer and 3,692 controls,Schwartz and Swanson (1997)analyzed the extent to which disparities in lung cancer risks are due to differences in smoking behaviors. The findings indicated that in the age range of 55 to 84 years, African-American/white differences in lung cancer were accounted for almost completely by differences in cigarette smoking behaviors. However, among men in the 40–54 year age group, African-Americans were 2 to 4 times more likely than whites to develop lung cancer even after controlling for smoking behaviors. The authors conclude that younger African-Americans may be especially susceptible to lung carcinogens or they may have unique exposures that remain unknown.
Socioeconomic status differences in smoking have been docu- mented (Gulliford, et al., 2003; Lund and Lund, 2005). In a survey of persons with diabetes mellitus in a socioeconomically deprived area of London, Gulliford, et al. (2003) found that smokers were more likely than non-smokers to come from low-socioeconomic status backgrounds. Lund and Lund (2005), using a study of 5,125 persons, showed that smokers were more likely to have lower socioeconomic status than non-smokers. In lower socioeconomic status groups, larger number of people smoked and they were likelyto smoke more dangerous cigarettes than those in the higher socioeconomic status groups. Young people begin smoking earlier and passive smoking is more acceptedin the lower socioeconomic status groups.
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Recently, there has been a relative increase of lung cancer of the adenocarcinoma type compared to the squamous cell carci- noma type, and this trend may be due to a shift from non-filter to filter cigarettes. Based on a case-control study of 356 patients with lung cancer and 162 control subjects, Marugame, et al. (2001) reported a decrease in both squamous cell carcinoma and adeno- carcinoma among lifelong smokers of filter cigarettes. There was more of a reduction in cases of squamous cell carcinoma than for adenocarcinoma. However, among men, under 54 years of age, those who only smoked filter cigarettes had an increased risk of adenocarcinoma, but a risk reduction in squamous cell carcinoma.
The researchers suggest that the change in histological type of lung cancer from squamous cell carcinoma to adenocarcinoma, espe- cially among young smokers, may be associated with changes in the type of cigarettes smoked.
The tar yields of cigarettes also have been examined to deter- mine if medium tar filter cigarettes are associated with a higher risk of lung cancer than low or very low tar cigarettes. Harris, et al. (2004)evaluated the relationship between thetar rating of the cigarette brand smoked in 1982 and lung cancer mortality in the following six years. The investigators discovered that regardless of the tar level of their current brand of cigarettes, all current smokers had a much higher risk of lung cancer than those who had stopped smoking or had never smoked. However, lung cancer risk was higher among female and male smokers of high-tar, non-filter brands compared to smokers of medium-tar, filter brands. In addi- tion, the results showed no differences in lung cancer risks among male and female smokers of very low-tar or low-tar brands com- pared to smokers of medium-tar brands. The authors conclude that men and women who smoke high-tar, non-filter cigarette brands have an even higher risk of lung cancer than those who smoke medium-, low-, or very low- tar-filter brands.
Air Pollution
A number of studies have discovered a link between air pol- lution, including both outdoor and indoor air pollution, and lung cancer as well as ischemic heart disease and respiratory diseases in
non-smokers (Whitrow, et al., 2003; Nafstad, et al., 2003; Boffetta and Nyberg, 2003). Nafstad, et al. (2003) foundhigher rates of lung cancer in urban areas, compared to rural areas, and the detection of known carcinogens in the urban atmosphere has led to the hypothesis that chronic air pollution increases lung cancer risk.
Investigators have discovered a causal relationship between exposure to environmental-tobacco smoke or second-hand smoke and lung cancer incidence. It is estimated that persons exposed to environmental tobacco smoke have a relative lung cancer risk of 1.2 (Boffetta and Nyberg, 2003).
However, exposure to environmental tobacco smoke is uneven in the population (Veglia, et al., 2003). Studies have evaluated determinants of exposure to environmental tobacco smoke to aid in the development of prevention programs. Veglia, et al. (2003) surveyed exposure to environmental tobacco smoke using a sample of 21,588 non-smokers in Italy. The researchers discovered that the most common exposure to environmental tobacco smoke comes from the workplace and individuals employed full-time were more exposed to environmental tobacco smoke than those employed part-time. The results also showed that white-collar employees had the highest exposures to environmental tobacco smoke.
Another known carcinogen, radon gas, can migrate from soils and rocks and accumulate in homes, underground mines, and other enclosed areas (Krewski, et al., 2005; Darby, et al., 2005;
Boffetta and Nyberg, 2003). Research reveals that underground miners who are exposed to high levels of radon gas decay prod- ucts (222Rn) have an elevated risk of developing lung cancer (Krewski, et al., 2005). Similar carcinogenic effects of exposure to radon decay products are demonstrated in experiments involving exposed laboratory animals (Field, et al., 2001).
Although high levels of radon produce an excess risk of lung cancer among underground miners, it is less clear if exposure to radon in homes results in a similar excess risk for lung cancer (Krewski, et al., 2005). Different factors may affect the association between residential-radon exposure and the risk of lung cancer.
Levels of radon vary within residences. Blot, et al. (1990), in their study of indoor radon and lung cancer in Shenyang, People’s Republic of China, found that radon levels weremore likely to be
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higher on the first floor of multiple-story residences or in single- story houses. In their study, radon levels were also higher in resi- dences which had coal-burning stoves that produced increased levels of indoor air pollution.
Several studies reveal a positive relationship between resi- dential-radon exposure and increased lung cancer risk (Darby, et al., 2005; Krewski, et al., 2005; Lubin, et al., 1995). Lubin, et al.
(1995) developed risk estimates based on pooling original data from 11 cohort studies of miners who were exposed to radon. The authors estimated that 10% of all lung cancer deaths may be a result of residential exposure to radon. In addition, 11% of lung cancer deaths among smokers and 30% of lung cancer deaths among persons who never smoked may be due to exposure to indoor radon.
Based on a combined analysis of 7 North American case- control studies, Krewski, et al. (2005) analyzed pooled data obtained from long-term alpha-track detectors to evaluate levels of residential radon. Using 3,662 cases and 4,966 controls, the inves- tigation discovered that the risks for lung cancer increased with res- idential radon concentration.
Darby, et al. (2005) evaluated the risk of exposure to residen- tial radon using data from 13 case-control studies of residential radon and lung cancer. The investigators discovered that for life- time non-smokers, the absolute risks of lung cancer by age 75 years would be approximately 0.4%, 0.5%, and 0.7% at usual radon con- centrations of 0, 100, and 400 Bq/m3 (becquerels or radon disinte- grations per second per cubic meter), respectively. Cigarette smokers had about 25 time greater absolute risks of lung cancer at the usual radon concentrations.
In phase 1 of the Iowa Radon Lung Cancer Study, Field, et al.
(2001) evaluated residential radon exposure using 413 incident lung cancer cases and 614 age-frequency matched controls. Their results indicated that cumulative exposure to radon in residences was positively related to increased lung cancer risk.
Other studies show that the precise effects of long-term radon exposure in residential settings are still not well known. A person’s smoking history and other confounding factors need to be con- trolled to evaluate the link between radon exposure and lung
cancer risk (Pearce and Boyle, 2005). Alavanja, et al. (1994)discov- ered that the magnitude of the risk for lung cancer from residen- tial radon exposure in the U.S. seems low. An investigation in the People’s Republic of China by Blot, et al. (1990) did not found a positive relationship between residential exposure to radon and lung cancer risks.
Research has documented that women in several Asian popu- lations are at increased risk for developing lung cancer from cooking and heating (Boffetta and Nyberg, 2003). However, some investigations have yielded only modest evidence for causality (Whitrow, et al., 2003).
In one follow-up study of a cohort of 38,866 female and 6,824 male hairdressers, Czene, et al. (2003) showed that female hair- dressers had an increased risk for lung cancer.
Arsenic
Studies have shown that consumption of water high in arsenic contamination increases the risk of lung cancer as well as the risk of bladder and skin cancer. Millions of people in Bangladesh, West Bengal India, and many other places around the world, are drink- ing ground water containing high concentrations of arsenic (Hossain, et al., 2005; West Bengal, India, and Bangladesh Arsenic Crisis Information Centre,2003; Frisbie, et al., 2002). In Bangladesh, people had used to drink surface water, which often was contam- inated with bacteria causing a range of diseases such as diarrhea, cholera, and typhoid (Frisbie, et al., 2002). Since independence in 1971, millions of tubewells were installed so that groundwater would be used for drinking instead of surface water. The use of groundwater reduced deaths from waterborne pathogens.
However, it has been discovered that large areas of of Bangladesh now are exposed to arsenic and other toxic elements in the ground- water. Frisbie, et al. (2002) discovered that chronic arsenic poison- ing may be the most important health risk from drinking Bangladesh’s tubewell water. In their study, arsenic concentrations in the tubewell water samples were found to ranged from less than 0.007 to 0.64mg/L, and 48% of the water samples had arsenic
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concentrations above 0.01mg/L, which is the drinking water guideline established by World Health Organization. The survey also found that the groundwater contained unsafe levels of man- ganese, lead, nickel, and chromium, and four adjacent, populated states in India may have groundwater with unsafe levels of arsenic and other toxic elements.
Asbestos
Instances of asbestos contamination in public water supplies have triggered studies to evaluate the environmental health effects of asbestos contamination (Browne, et al., 2005; Andersen, 1993;
Howe, et al., 1989). For example, very high concentrations of asbestos leachate in the drinking water in Woodstock, New York, were found in 1985. However, environmental health studies in the Woodstock, New York, area have not revealed a link between expo- sure to asbestos in drinking water and increased cancer incidence (Browne, et al., 2005). In fact, one study of the Woodstock, New York, area found the incidence of lung cancer was lower than expected for both women and men (Howe, et al., 1989).
Physical Activity
Several studies have shown that physical activity reduces lung cancer risk. For example, a population-based case-control study of 2,128 patients with lung cancer and 3,106 population controls in Canada found that recreational physical activity reduced the risk of lung cancer (Mao, et al., 2003). Both men and women who par- ticipated in physical activity had a reduced risk for lung cancer. A greater reduction in risks occurred for womenwith squamous cell carcinoma, while there was a greater reduction in risks among men for small cell carcinoma. Furthermore, smokers and those with low and moderate body mass indexes exhibited a greater risk reduction for lung cancer. The researchers recommend that more research is needed to substantiate the link between physical activity and his- tologic sub-types of lung cancer and gender as well as the biologic etiology (Varo Cenarruzabeitia, et al., 2003).
Nutrition and Lung Cancer
Some investigations show that the consumption of certain foods, such of fruit and vegetables, dietary supplements, and vita- mins may protect against lung cancer (Miller, et al., 2004; Mannisto, et al., 2004). For example, foods high in beta-cryptoxanthin, such as citrus fruit, may lower the risk of lung cancer. However, other investigations using cohort and case-control study designs have reported no protective effects. Intervention studies have demonstrated that supplemental beta-carotene has either no beneficial effect or a harmful impact on risk of lung cancer (Mannisto, et al., 2004). However, until recently research has been limited by the lack of databases for specific types of carotenoids.
Using data from 478,021 persons who participated in the Euro- pean Prospective Investigation into Cancer and Nutrition, Miller, et al. (2004) discovered that fruit consumption was associated with a reduced risk of lung cancer. This relationship was significant after controlling for age, smoking, height, weight, and gender. The asso- ciation between fruit consumption and lower lung cancer risk was strongest among persons from the Northern Europe centers, among current smokers, and was enhanced when 293 persons with lung cancer diagnosed in the first two years of follow-up were not used in the analysis. The researchers reported no relationship between consumption of vegetables or subtypes of vegetables and risk of lung cancer. However, the impact of fruit consumption on lung cancer risk is probably small compared to the effect of smoking cessation.
Breast Cancer
There are multiple risk factors for breast cancer and pre- malignant breast cancer (Tyrer, et al., 2004). Some of these factors are genetic and are associated with family history, while others are personal, lifestyle or environmental/occupational factors (Tyrer, et al., 2004). Various studies focus on the interactions between genetic susceptibility and environmental exposure in the etiology of breast cancer (Bernstein, et al., 2004; Millikan, et al., 2004).
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Genetic Factors and Family History of Breast Cancer
Genetic factors increase a woman’s risk of developing breast cancer (Tyrer, et al., 2004; Colditz, et al., 2004). Mutations in the BRCA1 or BRCA2 genes are possible precursors of breast cancer.
In southern Sweden,Loman, et al. (2001) evaluated the nature and prevalence of two germline mutations in a population-based series of early-onset breast cancer. Their results indicated that 48% of the women in the study with early-onset breast cancer have hadsome positive history of breast or ovarian cancer. BRCA1 or BRCA2 germline mutations were found in 9% of the women with early- onset breast cancer. Mutation carriers were more prevalent among young women with at least one or more first- or second-degreerel- atives with breast or ovarian cancer, and among women with bilat- eral breast cancer.
BRCA1 and BRCA2 mutations do not account for all of the familial aggregation of breast cancer (Tyrer, et al., 2004). The RPS6KB1 gene is enhanced and over expressed in about 10% of breast cancers and has been related to a poor prognosis of the disease (van der Hage, et al., 2004).
Han, et al. (2004) found that a human sulfotransferase (SULT1A1), which activates the sulfation of different phenolic and estrogenic compounds, predicted increased breast cancer risk in Chinese women. Zheng, et al. (2004) suggest that CYP11A gene polymorphism may increase susceptibility to breast cancer risk.
Other research focuses on the gene-environment interaction in influencing the risk of breast cancer. For example, the manganese superoxide dismutase (MnSOD) gene may increase breast cancer risk if specific environmental exposures, such as smoking, radia- tion to the chest, and occupational exposure to ionizing radiation, are present (Millikan, et al., 2004).
Benign Breast Disease
Research has revealed that a history of benign breast disease is related to an elevated risk of breast cancer (Wang, et al., 2004;
Altaf, et al., 2004; Colditz, et al., 2004). More research is needed to clarify this relationship, especially the ways in which the type of