Progress in understanding breast cancer: epidemiological and biological interactions

Update on cancer control in women

The global cancer burden in women appears to have stabilized according to the most recent estimates available although the distribution of cancer types appears to be changing with a sharp contrast between the increase in the absolute numbers of breast cancers and a decline in cervix cancers. Prospects for cancer control in women appear to be good within our current knowledge and deserve close attention. Rates of lung cancer in women are increasing substantially in many countries and seem set to overtake breast cancer as the commonest form of cancer death in women in many parts of the world. These changes are due to the effects of cigarette smoking, a habit which women widely embraced during the second half of the last century. The high levels of smoking currently in young women, which have yet to have their full impact on death rates, constitute an important hazard not only for future cancer risks but for several other important causes of death. There is strong and consistent evidence that increased consumption levels of fruit and vegetables is associated with reduced risks of many common forms of cancer including breast cancer. Although the breast is the commonest form of cancer in women in most western countries, the etiology of this disease remains elusive and preventable causes remain to be identified. Endogenous hormones also appear to have a role in cancer risk in women: oral contraceptives seem to increase slightly the risk of breast cancer in users in the use and in the immediate post-use period, but 10 years after cessation the risk again returns to that of never users. Oral contraceptive usage also appears to be protective against ovarian and endometrial cancer. The use of hormonal replacement therapy (HRT) appears to increase the risk of endometrial cancer and a positive association with breast cancer risk appears to exist. Within our current knowledge of the epidemiology of cancer in women, the most important preventive strategies would appear to be the prevention of cigarette smoking and increased dietary intake of vegetables and fruits. Screening has also shown to be effective in reducing incidence and mortality of cervix cancer and mortality from breast cancer. Although more work is needed, it is becoming clear that there could be an important role of HPV testing to further enhance cervix cancer screening. There are important variations in survival from a variety of cancers which are due to factors unrelated to the tumor behavior and that there are significant variations in survival from cancer. Reduction of these gaps could lead to a reduction in cancer mortality and contribute towards increased prospects for cancer control in women.

Meta-analysis of studies on breast cancer risk and diet: the role of fruit and vegetable consumption and the intake of associated micronutrients

A meta-analysis was carried out, in order to summarise published data on the relationship between breast cancer, fruit and vegetable consumption and/or the intake of beta-carotene and vitamin C. Relative risks were extracted from 26 published studies from 1982 to 1997. Random and fixed effects models were used. Between studies, heterogeneity was found for vegetables, fruit, vitamin C but not for beta-carotene. Summary relative risk (RR) estimates based upon a random effects model, except for beta-carotene, for 'high consumption' compared with 'low consumption', derived from the studies satisfying the inclusion criteria were as follows: vegetable consumption: RR=0.75 (95% CI (confidence interval) 0.66-0.85) from 17 studies; fruit consumption: RR=0.94 (95% CI 0.79-1.11) from 12 studies; vitamin C: RR=0.80 (95% CI 0.68-0.95) from 9 studies; beta-carotene: RR=0.82 (95% CI 0.76-0.91) from 11 studies. This analysis confirms the association between intake of vegetables and, to a lesser extent, fruits and breast cancer risk from published sources. Increasing vegetable consumption might reduce the risk of breast cancer.

Risk factors for breast cancer in nulliparous women

The relation between hormonal and lifestyle factors and breast cancer risk in nulliparae was investigated using data from two case-control studies conducted in Italy between 1983 and 1994. The study included 1041 nulliparae with histologically confirmed incident breast cancer and 1002 nulliparous controls admitted to hospital for a wide range of acute, non-neoplastic, nonhormone-related diseases. In premenopausal nulliparae, there was an inverse relation with age at menarche [odds ratios (OR) 0.45; 95% confidence intervals (CI) 0.24-0.86 for > or = 15 years vs < 12], while no association emerged in postmenopausal. Breast cancer risk increased with age at menopause, the OR being 1.91 (95% CI 1.26-2.90) for nulliparae reporting age at menopause > or = 53 years compared with < 45. Abortion was not related to breast cancer risk, the OR being 0.92 for any spontaneous, 0.97 for any induced and 0.77 for > or = 2 total abortions compared to none. The OR was 1.75 (95% CI 1.03-2.97) for women reporting their first abortion at age > or = 30 years compared with < 30. Oral contraceptives and hormone replacement therapy in menopause were moderately related to risk. The OR was 2.71 (95% CI 1.85-3.95) in nulliparae with a family history of breast cancer and 1.60 (95% CI 1.20-2.14) in those with a history of benign breast disease. Compared with nulliparae reporting a low physical activity, the OR was 0.79 (95% CI 0.54-1.16) for those reporting intermediate/high activity. Breast cancer risk increased with total energy intake, the OR being 1.65 (95% CI 0.99-2.75) in the highest tertile; beta-carotene was inversely related to risk (OR 0.60, 95% CI 0.38-0.95) for the highest tertile. Thus, most risk factors for breast cancer in nulliparae were similar to those in women generally.

Sociodemographic characteristics, smoking, medical and family history, and breast cancer

The relationship between sociodemographic characteristics, lifestyle, family history of cancer, medical history, and reproductive factors and breast cancer was investigated in a population-based case-control study of French Canadians in Montreal. In this study, a total of 414 French-Canadian cases and 429 age- and language-matched population controls were interviewed. Ever-married women showed significantly lower risk (OR: 0.64 [0.45-0.92]) for breast cancer, as did smokers (OR: 0.73 [0.55-0.98]), particularly of nonfilter cigarettes (OR: 0.36 [0.17-0.72]). Weight history, both for the year before the diagnosis of breast cancer and 10 years previously, was associated with risk for the disease. A strong inverse relationship was found between the number of full-term pregnancies (OR: 0.48 [0.28-0.82]) and the risk of breast cancer, while the p trend for late age at first pregnancy (p = 0.02) and menopause (p = 0.004) was statistically significant. A history of breast problems (OR: 1.87 [1.34-2.60]) and a history of breast cancer in relatives (OR: 2.95 [1.63-5.34]) were strongly associated with risk. This study confirms the risk factors of late age at first full-term pregnancy, nulliparity, late age at menopause, and positive family history of breast cancer in the etiology of this disease. Perhaps the protective effect of smoking against breast cancer could be due to its antiestrogenic influence.

Medical risks for women who drink alcohol

OBJECTIVE

To summarize for clinicians recent epidemiologic evidence regarding medical risks of alcohol use for women.

METHODS

MEDLINE and PsychINFO, 1990 through 1996, were searched using key words "women" or "woman," and "alcohol." MEDLINE was also searched for other specific topics and authors from 1980 through 1996. Data were extracted and reviewed regarding levels of alcohol consumption associated with mortality, cardiovascular disease, alcohol-related liver disease, injury, osteoporosis, neurologic symptoms, psychiatric comorbidity, fetal alcohol syndrome, spontaneous abortion, infertility, menstrual symptoms, breast cancer, and gynecologic malignancies. Gender-specific data from cohort studies of general population or large clinical samples are primarily reviewed.

MAIN RESULTS

Women develop many alcohol-related medical problems at lower levels of consumption than men, probably reflecting women's lower total body water, gender differences in alcohol metabolism, and effects of alcohol on postmenopausal estrogen levels. Mortality and breast cancer are increased in women who report drinking more than two drinks daily. Higher levels of alcohol consumption by women are associated with increased menstrual symptoms, hypertension, and stroke. Women who drink heavily also appear to have increased infertility and spontaneous abortion. Adverse fetal effects occur after variable amounts of alcohol consumption, making any alcohol use during pregnancy potentially harmful.

CONCLUSIONS

In general, advising nonpregnant women who drink alcohol to have fewer than two drinks daily is strongly supported by the epidemiologic literature, although specific recommendations for a particular woman should depend on her medical history and risk factors.

Estrogenic and antiproliferative properties of genistein and other flavonoids in human breast cancer cells in vitro

Experimental and epidemiologic studies support the view that soyfoods prevent cancer as well as diseases and symptoms associated with estrogen deficiency. Recent research suggests that the isoflavonoid genistein, a phytoestrogen found in abundance in soyfoods, may be one of the principal molecular components responsible for these health benefits. In this study we investigated the effects of a broad physiologically relevant concentration range of genistein on estrogen receptor (ER) binding, induction of the estrogen-regulated antigen pS2, and cell proliferation rate in ER(+) and ER(-) human breast cancer cells grown in vitro. Dose response to genistein was compared with that of estradiol, tamoxifen, and several other structurally similar iso- and bioflavonoids (e.g., equol, kaempferol, and quercetin). Our results revealed that genistein has potent estrogen agonist and cell growth-inhibitory actions over a physiologically achievable concentration range (10 nM-20 microM). Other flavonoids over the same concentration range were good estrogen agonists and poor cell growth inhibitors (equol) or poor estrogen agonists and potent growth inhibitors (kaempferol and quercetin). The growth-inhibitory actions of flavonoids were distinctly different from those of triphenyl antiestrogens like tamoxifen. In summary, our results reveal that genistein is unique among the flavonoids tested, in that it has potent estrogen agonist and cell growth-inhibitory actions over a physiologically relevant concentration range.

Reproductive factors and breast cancer risk. Effect of age at diagnosis

The data from a French case-control study of 495 patients with breast cancer and 542 control subjects interviewed in five French public hospitals, were analyzed to assess the effect of reproductive factors (age at menarche, age at first full-term pregnancy, the time interval between these two ages, and parity) on the risk of breast cancer. Age at menarche, age at first full-term pregnancy, the time interval between these two ages, and parity appeared to have a limited influence on breast cancer risk. However, the relationship between these factors and the risk of breast cancer varied according to the age at breast cancer diagnosis. In the youngest group of women, the most consistent effects came from factors occurring early in life (menarche, first full-term pregnancy, and consequently the time interval between these two events). These factors had a null or weak effect on the oldest group of women. The protective effect of high parity was confined to the oldest group of women.

Aging, comorbidity, and breast cancer survival: an epidemiologic view

This is a review of epidemiologic studies, which suggest that comorbidity (e.g., diabetes and heart disease) has an adverse effect on survival among women with incident, invasive breast cancer, adjusting for chronological age and stage of breast cancer at diagnosis. As part of this review, recent results are presented from a series of 463 breast cancer cases, identified through the Metropolitan Detroit Cancer Surveillance System. Women with two or more concurrent health conditions were 2.2 times more likely than breast cancer cases without comorbidity to die from their breast cancer over a four-year period (95% CI: 1.13, 4.18). Limiting heart disease was especially problematic. Recommendations are made for future research in this area.

Effect of dietary fatty acid composition on inositol-, choline- and ethanolamine-phospholipids of mammary tissue and erythrocytes in the rat

The present study investigated the effect of feeding maize-oil, olive-oil and fish-oil diets, from weaning to adulthood, on rat mammary tissue and erythrocyte phospholipid fatty acid compositions. Effects of diet on the relative proportions of membrane phospholipids in the two tissues were also investigated. Mammary tissue phosphatidylinositol (PI) fatty acids were unaltered by diet, but differences in phosphatidylethanolamine (PE) and, to a lesser extent, phosphatidylcholine (PC) fractions were found between animals fed on different diets from weaning. Differences observed were those expected from the dietary fatty acids fed; n-6 fatty acids were found in greatest amounts in maize-oil-fed rats, n-9 in olive-oil-fed rats, and n-3 in fish-oil-fed rats. In erythrocytes the relative susceptibilities of the individual phospholipids to dietary modification were: PE > PC > PI, but enrichment with n-9 and n-3 fatty acids was not observed in olive-oil- and fish-oil-fed animals and in PC and PE significantly greater amounts of saturated fatty acids were found when animals fed on olive oil or fish oil were compared with maize-oil-fed animals. The polyunsaturated:saturated fatty acid ratios of PE and PC fractions were significantly lower in olive-oil- and fish-oil-fed animals. No differences in the relative proportions of phospholipid classes were found between the three dietary groups. It is suggested that differences in erythrocyte fatty acid composition may reflect dietary-induced changes in membrane cholesterol content and may form part of a homoeostatic response the aim of which is to maintain normal erythrocyte membrane fluidity. The resistance of mammary tissue PI fatty acids to dietary modification suggests that alteration of PI fatty acids is unlikely to underlie effects of dietary fat on mammary tumour incidence rates.

Breast cancer and smoking, vodka drinking and dietary habits. A case-control study

The relationship between cigarette smoking, vodka drinking and consumption of 44 food items typical of the Polish diet were analysed in a case-control study in Cracow, Poland, among 127 cases of breast cancer and 250 controls randomly selected from the general population. Cigarette smoking was not significantly influencing the breast cancer risk. Compared with never-drinkers, the habit of vodka drinking 20 years earlier significantly increased breast cancer risk in women below 50 years of age (multivariate OR was 4.4 with 95% CI 1.6-12.4). Frequent consumption of boiled vegetables 20 years earlier (greater than 3 times per week) was associated with a decreased risk of breast cancer in women aged 50 years and more (multivariate OR was 0.4 with 95% CI 0.2-0.8).

Diet and prostatic cancer: a case-control study in northern Italy

The relationship between intake of various indicator foods and beverages and risk of prostatic cancer was assessed in 271 cases of prostatic cancer and 685 hospital controls recruited in two areas of northern Italy, the province of Pordenone and the greater Milan area. Increased risks were found for more frequent intake of meat [odds ratio (OR) in the highest vs. lowest consumption tertile = 1.4, 95% confidence interval (CI) 1.0-2.0], milk (OR = 1.6, 95% CI 1.1-2.4), fresh fruit (OR = 1.4, 95% CI 1.0-2.1), and vegetables (OR = 1.4, 95% CI 0.9-2.2). After allowance for the reciprocal confounding effect of various dietary habits, only frequent intake of milk seemed to be a significant independent indicator of prostatic cancer risk. There was also a clue that the unfavorable influence of frequent intake of a few food items (i.e. meat, fish, liver, ham and salami, milk and butter, and retinol) may be greater or restricted to older individuals (i.e., > or = 70 yrs of age). In conclusion, the present study confirms the presence of a moderate adverse effect of high intake of foods of animal origin, chiefly milk, while it suggests that a diet rich in fresh fruit and vegetables does not convey a protection.

Oral contraceptives and breast cancer. A review with some comments on mathematical models

The relationship between oral contraceptive use and breast cancer is discussed on the basis of information given in review articles, meta-analyses and editorials emphasizing methodological problems related to bias and confounding. Over the last few years a shift in opinion has taken place. Most reviewers now consider that long-term use of oral contraceptives is associated with an increased risk of premenopausal breast cancer and no effect among postmenopausal breast cancer. This result is compatible with an additive effect (in rate measure scale) of oral contraceptive use on breast cancer risk.

Combination of dietary factors in relation to breast-cancer occurrence

Combinations of dietary factors were studied in relation to breast-cancer occurrence among 133 breast cancer cases and 289 population controls in The Netherlands. Dietary factors were classified according to their possible mechanism of action, i.e., relating either to the intestinal microflora (total fat, fiber, fermented milk products) or to the anti-oxidant hypothesis (beta-carotene, selenium and polyunsaturated fatty acids). From 6 interactions evaluated, the combination of high fiber intake and high intake of fermented milk products was the only one suggesting synergistic protection (age-and-fat-adjusted OR for interaction = 0.48, 95% confidence interval (CI) = 0.21 - 1.13). In order to estimate the extent to which the above dietary factors together might be related to breast cancer, subjects with a supposedly favorable dietary pattern (low fat intake, high fiber intake, high intake of fermented milk products; high intake of beta-carotene and selenium, low intake of polyunsaturated fatty acids) were compared with subjects with an unfavorable dietary pattern. This resulted in an age-adjusted odds ratio of 0.40 (95% CI = 0.14 - 1.15), which was largely attributable to the combination of low intake of fat and high intake of fermented milk products and fiber (age-adjusted OR = 0.33, 95% CI = 0.15 - 0.73). The other factors did not appreciably affect the odds ratio. These analyses show in a quantitative way that a dietary pattern which combines low intake of fat and high intake of fiber and fermented milk products might provide substantial protection against breast cancer.

Number of children and death from hormone-dependent cancers

The association between number of children of current marriage reported by 431,604 women aged 45-74 years at the Norwegian Census in 1970 and mortality, at follow-up through 1985, from hormone-dependent cancers, i.e., cancers of breast, corpus uteri and ovary combined, has been investigated. The reduction in age-adjusted mortality was 9.6% (95% confidence interval; 8.3-10.9%) for each child with no deviation from linearity. Women with 8-11 children had a relative risk of 0.34 (0.25-0.47) compared to nullipara. Adjustment for age at first birth slightly changed the effect of number of children on mortality to 9.3% per child. The reduction in mortality per child was for cancer of the breast 7.2%, corpus uteri 12.2% and ovary 12.7%. Our findings indicate that having few children is a major risk factor for death from the 3 hormone-dependent cancers combined.

Anthropometric measures and breast cancer in young women

Body height and weight in relation to breast cancer in women younger than 45 years were investigated in a case-control study in Sweden and Norway. The study included 317 Swedish and 105 Norwegian cases diagnosed in 1984-85 with 317 Swedish and 210 Norwegian age-matched population controls. Neither height nor body size, measured as body mass index, was associated with breast cancer. Change in body mass from the age of 20 years to 18 months before the time of diagnosis (cases) or interview (controls) had no effect on breast cancer risk. The study provides no evidence that anthropometric measures are risk factors for breast cancer in young women, indicating that the postulated inverse relationship between body mass index and pre-menopausal breast cancer could be limited to peri-menopausal women.

Smoking and breast cancer risk in Denmark

The effect of smoking on breast cancer risk was evaluated in a population-based case-control study, including 1,480 women diagnosed with breast cancer in Denmark between 1983-84. They were identified from the files of the nationwide clinical trial of the Danish Breast Cancer Cooperative Group and the Danish Cancer Registry. The control group was an age-stratified sample of 1,332 women from the general population. Data on risk factors were collected by self-administered questionnaires. The risk of breast cancer among current smokers and ex-smokers was similar to that in non-smokers, both risk estimates being close to unity. No dose-response relation was observed for any measure of smoking (age at start, duration, number of cigarettes per day, or cigarette-years of exposure) in all subjects, and when pre- and post-menopausal women were examined separately. These findings suggest that smoking is not associated with the risk of breast cancer.

Incidence of cancer of the lung, stomach, breast, and cervix in the USSR: pattern and trends

The most frequent fatal malignant tumors in the Soviet Union are cancers of the lung, stomach, breast, and cervix uteri. From incidence statistics and population estimates provided by the Department of Statistics of the Ministry of Health, age-adjusted incidence rates for the period 1971-87, using the World standard population, have been computed for the USSR as a whole and for each of the 15 Soviet republics. For six republics believed to have the highest quality of data and relatively homogeneous populations, time-trends are examined over the period. There is important geographical variation in the incidence of malignant tumors in the Soviet Union. The differences between high and low incidence areas are four-fold for cancer of the lung and stomach, three-fold for cancer of the breast and two-fold for cancer of the cervix. Overall in the six republics for which time-trends are examined, cancers of the lung and breast have increased, cancers of the stomach and cervix have decreased. There are some variations in specific age groups in some republics.

Body height and risk of breast cancer. A prospective study of 23,831 Norwegian women

The association between body height and the incidence rate of breast cancer has been examined in 236 cases of breast cancer that occurred among 23,831 Norwegian women during 11-14 years of follow-up. At the time of height measurement they were 35-51 years of age. The age-adjusted incidence rate ratio (IRR) of breast cancer was 2.03 (95% of confidence limits 1.36 and 3.01) for women taller than or equal to 167 cm (mean = 170 cm) compared to women who were less than 159 cm (mean = 155 cm). The positive association with height was stronger among women who were diagnosed before the age of 51 (IRR = 2.63; 95% confidence limits 1.48 and 4.68), than among women diagnosed after this age. Moreover, the association appeared to be confined to women who had lived through their peripubertal growth during a period (1940-45) of nationally increased nutritional variability with reduction in dietary fat and restricted caloric intake. Among women born between 1929 and 1936, the relation with height displayed a strong positive linear trend (chi 2 trend = 13.4, P less than 0.001), which was not present among women born between 1925 and 1928 (chi 2 trend = 0.7, P = 0.40), nor among women born in 1937 or later (chi 2 trend = 1.5, P = 0.20). We hypothesise that a time-dependent diversity in nourishment, which may be of particular importance for women in their peri-menarcheal development, may explain the different association between body height and breast cancer risk that was observed for women in different birth cohorts.

Body mass index and risk of breast cancer. A prospective study of 23,826 Norwegian women

The association between body mass index (BMI) and the incidence rate of breast cancer has been examined in 236 cases of breast cancer that developed among 23,826 Norwegian women during 11 to 14 years of follow-up. At the time of height and weight measurement they were 35 to 51 years of age, and at the end of follow-up their age was between 46 and 63 years. There was an overall age-adjusted incidence rate ratio (IRR) of 0.52 (95% confidence limits, 0.34 and 0.77) for women in the highest quartile of BMI compared to women in the lowest quartile, which was confined to an effect observed among women who were diagnosed at age 50 or earlier (IRR = 0.36). The association with BMI displayed an inverse dose-related trend (chi 2 for trend = 14.22, p less than 0.001). The negative trend was particularly pronounced among non-smoking women (chi 2 = 14.63), and no clear trend associate with BMI was observed among women who smoked 10 or more cigarettes per day (chi 2 = 0.41), indicating an interaction between BMI and cigarette smoking (chi 2 interaction = 3.86, p = 0.05). We thus suggest that there is a negative association between body mass index and risk of breast cancer among premenopausal women.

Breast cancer risk and history of selected medical conditions linked with female hormones

The relation between history of several medical conditions and procedures and risk of breast cancer was evaluated in data from a hospital-based case-control study of 2663 cases of breast cancer and 2344 controls with acute conditions unrelated to any of the established or potential risk factors for breast cancer. Whereas previous diagnosis of diabetes mellitus, thyroid disease, hypertension at any age, hyperlipidaemia, cholelithiasis, pelvic inflammatory disease and physician-diagnosed subfertility were unrelated to cancer risk, history of severe obesity in postmenopausal women (odds ratio [OR] 1.4), benign breast disease (OR 1.8) and history of breast biopsies (OR 2.4) were associated with significant risk elevation. Conversely, lifelong history of menstrual irregularities (OR 0.6) seemed to confer some protection against onset of breast cancer. This study supports the hypothesis that, unlike endometrial cancer, breast cancer risk is not enhanced by medical conditions known or suspected to be linked with female hormones, with the exception of benign breast disease and severe overweight in postmenopausal women.

Reproductive factors and cancers of the breast, ovary and endometrium

In contrast to cancers of non-hormone-dependent sites, cancers of the breast, ovary and endometrium show a slowing down of the rate of increase in incidence at around age 50, as if ceasing menstrual activity reduced risk. Also nulliparous women appear more prone to these three cancers as compared to parous women, thus suggesting that pregnancies also represent a 'protected' time. Epidemiological studies on breast cancer, the only ones sufficiently large to try to disentangle meaningfully the effects of collinear reproductive variables such as parity and ages at first and last birth, show, however, that the effect of pregnancy is not simple and depends on how many births take place and at what age. Larger population-based investigations able to obtain with greater precision information not only on reproductive factors but also on possible confounding variables (e.g. socio-economic status, dietary habits, etc.) are mandatory, particularly as regards ovarian cancer and endometrial cancer. The lesson from the recent studies on pregnancy-related events and breast cancer is, however, that initially a decrease of old certainties must be expected to derive from the accumulation of new, better epidemiological data.

Exposure, susceptibility, and breast cancer risk: a hypothesis regarding exogenous carcinogens, breast tissue development, and social gradients, including black/white differences, in breast cancer incidence

At present, known risk factors account for only one-third of breast cancer cases diagnosed in the United States. They explain an even smaller fraction of the ten-fold variation in international breast cancer incidence rates. The low population-attributable risk of these identified risk factors, plus the existence of phenomena that cannot be easily explained by current etiologic hypotheses (such as the higher rate of breast cancer among black as compared to white women under age 40 within the United States), suggests that unidentified risk factors contribute substantially to breast cancer causation. This paper summarizes evidence to propose that two socially-conditioned factors determine a society's breast cancer incidence and its social gradients in risk: 1) the extent of exposure to exogenous carcinogens, and 2) breast tissue susceptibility to these exposures. It is further hypothesized that breast tissue susceptibility is inversely related to breast tissue differentiation, and that socially-mediated reproductive patterns (involving both early-terminated and full-term pregnancies) affect susceptibility both by altering (via hormonally-mediated mechanisms) the number and ratio of undifferentiated and differentiated cells, and by stimulating the growth of initiated and transformed cells. This view is presented in contrast to hypotheses that propose exposure to endogenous hormones as the major determinant of breast cancer risk.