Nutrition and breast cancer

The two major epidemics of the twenty-first century: obesity and cancer

It is a well-known fact that severe obesity is associated with the metabolic syndrome, type 2 diabetes, cardiovascular disease, hypertension, and other diseases. Epidemiological studies have suggested that obesity is also associated with increased risk of several cancer types. The number of people who are suffering from severe obesity is growing, and clinical data suggest that severely obese patients belong to a unique population with regards to risk, efficacy of screening, and cancer treatment. This review will point out the potential mechanism linking obesity and cancer and will discuss several challenges in various treatment modalities of cancer in obese patients.

Enhanced tumorigenesis in p53 knockout mice exposed in utero to high-dose vitamin E

The limited antioxidative capacity of the embryo and fetus may increase their risk for cancer initiation and/or promotion by reactive oxygen species (ROS)-mediated oxidative DNA damage and/or signaling. To determine if cancer can originate in utero, a high dietary dose of the antioxidant vitamin E (VE) (10% dl-alpha-tocopherol-acetate) was given to cancer-prone p53 knockout mice throughout pregnancy. Although reducing fetal death (P < 0.05), in utero exposure to VE enhanced postnatal tumorigenesis in both +/- (P < 0.04) and -/- (P < 0.0008) p53-deficient offspring. VE did not alter maternal weights, offspring p53 genotypic distribution or tumor spectrum. Constitutive embryonic DNA oxidation in untreated -/- p53 embryos [gestational day (GD) 13] was higher than in +/- and +/+ p53 littermates (P < 0.05). VE reduced DNA oxidation in -/- p53 embryos (P < 0.05) without affecting +/- and +/+ p53 littermates. VE had contrasting, tissue-dependent effects on fetal (GD 19) DNA oxidation, with reductions in -/- and +/- p53-deficient fetal brains (P < 0.01), increases in skin (P < 0.05) and no effect in liver and thymus. The 250-fold increase in dietary VE levels produced only 1.6-6.3-fold, tissue-dependent increases in tissue concentrations. The greatest increase, in fetal skin, correlated with increased DNA oxidation in that tissue in -/- and +/- p53-deficient fetuses and enhanced tumorigenesis in these genotypes. These results show that some cancers may originate in utero and the risk can be enhanced by embryonic and fetal exposure to high dietary levels of VE. The elevated DNA oxidation in some tissues of untreated -/- p53 offspring suggests that ROS may contribute to their higher baseline tumor incidence. The limited and tissue-dependent disposition of VE indicates substantial conceptal regulation. The similarly selective and contrasting effects of VE on DNA oxidation may contribute to its controversial protective efficacy and suggest that its effects on tumorigenesis are cell-specific, possibly in high doses involving a pro-oxidative mechanism.

Dietary polyunsaturated n-6 lipids effects on the growth and fatty acid composition of rat mammary tumors

The aim of this study was to analyze the effects of a polyunsaturated n-6 high-fat diet on rat DMBA-induced breast cancer at different stages of the carcinogenesis and to investigate if changes in the tumor fatty acid composition are one of the mechanisms by which dietary lipids could exert their effects. 14 fatty acids were evaluated in 6 lipid fractions. The results firstly showed that this high-fat diet stimulated the malignant mammary tumor growth, mainly all in the promotion group. The tumor lipid analysis indicated: 1) that each lipid fraction presented distinct major fatty acids (>5%) which were not the most abundant in the diet, except in the case of the triacylglicerides, suggesting the different resistance to dietary fatty acid modification of the tumor lipid fractions; 2) a higher arachidonic acid content in the fractions with less linoleic acid, above all in phospholipids, particularly in the phosphatidylethanolamine, indicating a different efficiency of conversion; 3) the three most abundant fatty acids in the dietary lipid (18:2n-6, 18:1n-9 and 16:0) were those which essentially displayed the differences between groups; thus, the high-fat diet changed the tumor lipid profile, increasing the 18:2n-6 relative content and decreasing that of the 18:1n-9; differences were significant in phosphatidylcholine, free fatty acids and triacylglycerides. Any change was obtained in the phosphatidylinositol. The greatest number of differences was found in the promotion group. Taken as a whole, our results suggest the different roles of lipid fractions in breast cancer cells and an association between cancer malignancy and the content of linoleic and oleic acids.

A clinical trial to selectively change dietary fat and/or energy intake in women: the Women's Diet Study

Dietary fat and energy intake have been implicated in breast cancer etiology. To examine the relative importance of these dietary factors on markers of cancer risk in women, we designed an intervention trial to selectively decrease fat and/or energy intake in free-living, premenopausal women who were somewhat overweight. The study used a 2 x 2 factorial design to evaluate the independent and interactive effects of dietary fat and energy. The diets were nonintervention, low fat (15% of energy from fat, maintenance of energy intake), low energy (25% energy reduction), and combination low fat and low energy. We utilized an individualized counseling approach with self-selection of foods. Women on the low-fat and combination diets were asked to meet given daily goals for fat grams and food group exchanges, while women on the low-energy diet used only food group exchanges. Of the 113 premenopausal women randomized who were eligible for analysis, 43% were African-American. A total of 88 women completed the 12-week program, and adherence to the dietary goals was similar in both racial groups. Women on the low-fat diet were able to reduce dietary fat intake to 19% of energy by 4 weeks and to 17% by 12 weeks with a slight decrease in energy intake. Women on the low-energy diet met their energy reduction goals by four weeks while maintaining percentage of energy from fat. Women on the combination diet largely met their goals by four weeks as well. These data indicate that it is possible to selectively manipulate dietary fat and energy intake in women over a short period of time, which makes clinical studies on the relative effects of these two dietary variables on cancer risk biomarkers readily feasible.

High fat diet induced oxidative DNA damage estimated by 8-oxo-7,8-dihydro-2-deoxyguanosine excretion in rats

The role of dietary fats and energy in carcinogenesis has been partly related to oxidative damage to DNA. We have investigated the effect of dietary fat content and saturation on the urinary excretion of 8-oxo-7,8dihydro-2'-deoxyguanosine (8-oxodG) in male and female rats. Groups of Fischer F344 rats (n = 6-10) were fed control chow (3.4% fat) or diets containing 21.8% corn oil or 19.8% coconut oil + 2% corn oil for 12-15 weeks. At the end of the diet intervention period 24h urine was collected for determination of 8-oxodG by HPLC. In the male groups fed control, corn oil and coconut oil diet the excretion of 8-oxodG was 403+/-150, 932+/-198 and 954+/-367pmol/kg 24 h, respectively (p < 0.05). In the female groups fed control and corn oil diet the excretion of 8-oxodG was 752+/-80 and 2206+/-282 pmol/kg 24 h, respectively (p < 0.05). Calculated per whole animal the excretion was 137+/-51, 324+/-70 and 328+/-128 pmol/24 h in the control, corn and coconut oil male groups and 156+/-21 and 464+/-56 pmol/24 h in the control and corn oil female groups, respectively ( p < 0.05). Thus, per animal or per consumed energy there was much less difference in 8-oxodG excretion between the corresponding male and female groups and only significant difference between the high fat groups. There was a close correlation (r = 0.7; p < 0.05) between 8-oxodG excretion and the energy intake. The present study suggests that a high fat diet increases oxidative DNA modification substantially irrespective of the saturation level of the fat. Energy intake appears to be the major determinant of the rate of modification.

Breast cancer: aetiological factors and associations (a possible protective role of phytoestrogens)

BACKGROUND

In spite of many known and suspected factors associated with the risk of breast cancer there has until recently been no explanation for its continuing increase in women of Western societies over recent decades or why there has not been an equivalent increase in women of most Asian and other less Westernized societies. It has long been suspected that a significant factor has been an increasing change of diet in Western societies from one predominantly vegetarian to one with a high content of meat and dairy products as well as 'refined' foods. Although diet has long been suspected there has otherwise been no real explanation as to the mechanism of the change in incidence of breast cancer.

METHODS

A comprehensive literature review has been made of aetiological factors and associations concerning breast cancer to determine whether any consistent trend can explain the rising incidence in Western societies.

RESULTS

There are a number of likely contributory factors but there is now accumulating evidence that the single most important difference is that people having a vegetarian diet have a high intake of legumes and other plant foods containing a variety of lignans and isoflavonoids. These appear to have an important role as nature's sex hormone modulators. These agents appear to be biologically active in a number of ways not yet completely understood but they do have both a weak oestrogenic effect and an anti-oestrogenic competitive effect, thus reducing the potential carcinogenic action of prolonged oestrogen activity. A probable additional benefit of such diets could be the role of dietary fibre.

CONCLUSIONS

A major problem of Western diets may not be the presence of meat or dairy products in the diet but the absence of desirable ingredients of vegetarian diets, namely dietary fibre and certain plant lignans and isoflavonoids. A modification of diet to include a greater proportion of fibre and soy or other leguminous plant food should be studied. Alternatively addition of more fibre and lignans and especially isoflavonoids to traditional Western diets would seem worthy of serious investigation. Such influences appear to have their greatest impact early in life and therefore could be especially important for girls and young women in Western societies.

Modulation of oxidative DNA damage levels by dietary fat and calories

Decreased dietary intake of fat and/or calories generally results in a lower incidence of mammary gland tumors in rodents. Feeding of either low-fat or calorie-restricted diets to rats also has been shown to result in decreased levels of oxidative DNA damage. Since oxidative DNA damage is suggested to have a role in carcinogenesis, this may be one mechanism by which dietary change can reduce cancer risk. The effects of calorie-restricted diets on both oxidative DNA damage levels and mammary gland tumor incidence are generally more pronounced than that of low-fat diets. There is, however, some difficulty in defining what amount of fat should be used to prepare 'low-fat' and 'high-fat' rodent diets as well as what a suitable fat intake for control diets should be in studies that examine the effects of dietary fat and/or calories on tumorigenesis. In particular, the promoting effects of dietary fat may be exerted only up to a certain level of fat, above which no further effect is observed. Another difficulty in the interpretation of the results is that there may be a time-dependent effect of high fat diets on oxidative damage, with increased damage resulting only when the diets are fed for longer periods of time. The appropriate experimental approach to model human dietary exposures therefore remains to be determined. Although the effects of caloric intake on mammary gland tumorigenesis appear to be more pronounced than that of fat intake, low-fat diets still may be useful as a preventive measure in human populations to reduce breast cancer risk for individuals who cannot safely reduce their caloric intake.

Influence of esculetin on incidence, proliferation, and cell kinetics of mammary carcinomas induced by 7,12-dimethylbenz[a]anthracene in rats on high- and low-fat diets

The effects of a high-fat diet and esculetin were investigated on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis in female Sprague-Dawley rats. Rats were given a 5-mg dose of DMBA. Seven days later, they were fed either a high-fat (20% soybean oil) or low-fat (0.5% soybean oil) diet. A half of the rats received diets containing 0.03% esculetin. Esculetin significantly inhibited tumor incidence, growth and cell kinetics of the tumor in the rats fed the high-fat and the low-fat diets. Our findings indicate that DMBA-induced mammary tumorigenesis is affected by lipoxygenase products.

Dietary fat and breast cancer

High-fat diets are thought to increase the risk of breast cancer because animals develop mammary cancer more readily when they are fed high-fat compared to low-fat diets, and breast cancer incidence and mortality are higher in countries with high-fat as compared to those with low-fat diets. Prospective cohort studies and case-control studies have failed to provide much support for this theory, but such studies are less capable of showing the relationship because of smaller differences in dietary fat intakes of the study populations; difficulties in assessing the diets of individuals over a period of time; and possible differences in genetic susceptibility of cases and controls to breast cancer. Studies on migrants have shown that breast cancer incidence and mortality increase in populations who move from countries with low-fat to those with high-fat diets, indicating that observed geographical differences in breast cancer are due to environmental rather than genetic factors. This is supported by time-trend studies showing that breast cancer increases in countries as the level of fat in the diet rises. Controlled, long-term dietary trials are needed to determine whether the converse is true: namely, that reduction of dietary fat can reduce the risk of breast cancer. Large groups are required to achieve statistical significance, but smaller numbers may be adequate for studies on high-risk individuals. Preliminary experiments already have demonstrated the feasibility of carrying out such dietary trials.

Breast cancer risk factors. Contributions to planning breast cancer control

The analytic epidemiology of breast cancer has identified several risk factors that may be the bases for developing preventive interventions and refining screening guidelines. Breast cancer risk factors include both personal and environmental sources of risk. The available data, however, do not yet support the feasibility of large scale preventive interventions. Controlled trials will be needed to assess the effectiveness of those approaches. Knowledge of risk factors may be used by physicians to tailor their recommendations for individual patients. Risk factor data also may be used to modify screening recommendations for special populations. A family history of breast cancer may be a basis for modifying screening recommendations but this may be appropriate only for a subset of women with breast cancer in a relative.

Professional and consumer concerns about the environment, lifestyle, and cancer

Although it cannot be said that "everything causes cancer," our environment will never be carcinogen-free. As a result, there are many substances we come in contact with daily that could be potentially harmful to our health. Even with the growing knowledge of the mechanisms of carcinogenesis, it is difficult to single out the exact cancer-causing or -promoting effects of single substances. The confusion that exists about the environment, lifestyle, and cancer can be overwhelming for everyone. Garfinkel offered the following suggestions for health care providers to use in putting this issue into better perspective for consumers: (1) no single study of cancer risk factors should be used as a basis for writing or changing public health policy; (2) animal studies should be supportive of findings in epidemiological studies; (3) any environmental factor-cancer effect relationship should be demonstrated biologically; (4) regulatory agencies such as the EPA tend to be conservative in their interpretation of study results, and may suggest caution even when the risk of developing cancer is low; (5) regulatory agencies have been known to extrapolate future effects of carcinogen exposure from current incomplete or limited information about the carcinogen in question. With the knowledge that we do have, we must strive to take personal control over life-style factors that may cause cancer.

Adjuvant dietary fat intake reduction in postmenopausal breast cancer patient management. The Women's Intervention Nutrition Study (WINS)

Management of localized breast cancer now commonly involves a breast-sparing approach combined with systemic adjuvant therapy resulting in improved cosmetic results and patient survival. Reducing dietary fat intake represents a conceptually new approach to further improve outcome of patients with resected breast cancer. The rationale supporting evaluation of dietary fat reduction in the management of patients with localized breast cancer is based on: (1) epidemiologic observations (along with biochemical and hormonal correlates) of major differences in stage-by-stage survival of patients with localized breast cancer comparing outcome in countries with low fat (Japan) versus high fat (U.S.A.) dietary intakes; (2) relationships between dietary fat intake and factors prognostic of clinical outcome in patients with established breast cancer; (3) effects of weight gain (especially that associated with adjuvant chemotherapy) on breast cancer clinical outcome; (4) in vivo animal studies demonstrating adverse influence of increased dietary fat intake (especially linoleic acid) on growth and metastatic spread of mammary cancer; (5) direct adverse effects of increased linoleic acid on human breast cancer growth in vitro; (6) plausible mechanisms which could mediate the effects of dietary fat intake reduction on breast cancer growth and metastatic spread; (7) demonstration of adherence to dietary fat reduction regimens in ongoing clinical feasibility studies including those involving postmenopausal patients with resected breast cancer; and (8) favorable sample size requirements for definitive assessment of dietary fat intake reduction influence on breast cancer growth and metastases (using as endpoints relapse-free survival and overall survival) in postmenopausal breast cancer patients with localized disease.

Breast cancer: early diagnosis of precursor lesions and clinically inapparent carcinoma by fine needle aspiration

Breast cancer death rate has remained stable at 26 per 100,000 for over 50 years. This control failure is due in large part to difficulty in early diagnosis. Combined clinical evaluation, mammography and fine needle aspiration (FNA) offer the best opportunity for early diagnosis. Non-directed FNA is a useful adjunctive technique and three illustrative cases are presented. Cancer evolves from proliferative epithelial disease of ducts and lobules. Atypical duct hyperplasia in association with family history is a pertinent marker for development of cancer. Identification of hyperplastic lesions traditionally occurs after surgical biopsy and histopathologic review. FNA demonstrates patterns of both duct hyperplasia and atypical duct hyperplasia. Ploidy studies of such smears offer the possibility of selecting precancerous lesions for extirpation. A combination of directed and undirected punctures and ploidy studies may yield early diagnosis of precancerous lesions.

A proposed mechanism for effects of diet on mammary cancer

Growth and development of mammary glandular parenchyma appear to be strongly influenced by the associated adipose tissue. Because fat is the major form of energy storage in the body, any changes in energy balance will be reflected in the weight of adipose tissue to a greater extent than in body weight as a whole. High-fat diets tend to encourage energy storage and may promote mammary cancer by increasing the amount of adipose tissue in the gland. The intimate association of adipose and glandular tissue would facilitate the transfer of any growth-promoting substances, such as polyunsaturated fatty acids, eicosanoids, estrogens, or other growth factors, from the adipose to the glandular tissue. Conversely, low-fat diets or restriction of food intake may decrease the risk of mammary cancer by reducing the amount of adipose tissue and thus reducing exposure of the glandular tissue to such growth-promoting substances.