Diet and breast cancer in Shanghai and Tianjin, China

Mechanism for the suppression of the mammalian stress response by genistein, an anticancer phytoestrogen from soy

BACKGROUND

Soy products contain high levels of genistein, a phytoestrogen that is a potent inhibitor of cell proliferation and angiogenesis. Genistein has been found to inhibit the growth of carcinogen-induced cancers in rats and human leukemia cells transplanted into mice. The induction of stress proteins (e.g., glucose-related proteins and heat shock proteins) in tumor cells has been shown to protect them against programmed cell death; this stress response is inhibited by genistein. The mechanism(s) by which genistein affects certain stress response genes was explored in this study.

METHODS

Mammalian cell cultures were treated with azetidine, a proline analog, which elicits a stress response that includes the induction of the expression of glucose-regulated protein GRP78 and heat shock protein HSP70. The effects of azetidine and/or genistein treatment on cellular levels of grp78 and hsp70 messenger RNAs and proteins were measured by northern blot hybridization and western blot analyses, respectively, and the binding of nuclear factors to sequence motifs in the upstream (promoter) regions of these two genes were examined by electrophoretic mobility shift assays.

RESULTS

Genistein antagonized the binding of a specific transcription factor, nuclear factor-Y/CCAAT binding factor (NF-Y/CBF), to the CCAAT sequence element most proximal to the transcription start sites in the hsp70 and grp78 promoters; this CCAAT element was previously shown to be necessary for full-stress inducibility of both genes. Treatment of cells with genistein converted NF-Y/CBF into a nonbinding, transcriptionally inactive form.

IMPLICATION

The anticancer effects of genistein may be related to its ability to reduce the expression of stress response-related genes.

Decreased serum estradiol concentration associated with high dietary intake of soy products in premenopausal Japanese women

We examined the cross-sectional relationship of soy product intake to serum concentrations of estradiol (E2) and sex hormone-binding globulin (SHBG) in 50 healthy premenopausal Japanese women. Intakes of soy products and various nutrients were estimated through a semiquantitative food-frequency questionnaire. Blood samples were drawn from each subject on Days 11 and 22 of her menstrual cycle. The intake of soy products was inversely correlated with E2 on Days 11 and 22 of the cycle after controlling for age, body mass index, cycle length, and intakes of total energy, fat, and crude fiber (r = -0.23, p = 0.08 and r = -0.32, p = 0.04, respectively). No significant correlation was observed between soy product intake and SHBG. There was a tendency for the intake of individual soy foods such as tofu and miso to be inversely correlated with E2 on Days 11 and 22 of the menstrual cycle. Miso intake was inversely significantly correlated with SHBG on Day 22 of the cycle (r = -0.36, p = 0.02). If the observed association is causal, our results suggest that the consumption of soy products lowers the risk of developing breast cancer risk modifying estrogen metabolism.

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.

Case-control study of phyto-oestrogens and breast cancer

BACKGROUND

Phyto-oestrogens are a group of naturally occurring chemicals derived from plants; they have a structure similar to oestrogen, and form part of our diet. They also have potentially anticarcinogenic biological activity. We did a case-control study to assess the association between phyto-oestrogen intake (as measured by urinary excretion) and the risk of breast cancer.

METHODS

Women with newly diagnosed early breast cancer were interviewed by means of questionnaires, and a 72 h urine collection and blood sample were taken before any treatment started. Controls were randomly selected from the electoral roll after matching for age and area of residence. 144 pairs were included for analysis. The urine samples were assayed for the isoflavonic phyto-oestrogens daidzein, genistein, and equol, and the lignans enterodiol, enterolactone, and matairesinol.

FINDINGS

After adjustment for age at menarche, parity, alcohol intake, and total fat intake, high excretion of both equol and enterolactone was associated with a substantial reduction in breast-cancer risk, with significant trends through the quartiles: equol odds ratios were 1.00, 0.45 (95% CI 0.20, 1.02), 0.52 (0.23, 1.17), and 0.27 (0.10, 0.69)--trend p = 0.009--and enterolactone odds ratios were 1.00, 0.91 (0.41, 1.98), 0.65 (0.29, 1.44), 0.36 (0.15, 0.86)--trend p = 0.013. For most other phytoestrogens there was a reduction in risk, but it did not reach significance. Difficulties with the genistein assay precluded analysis of that substance.

INTERPRETATION

There is a substantial reduction in breast-cancer risk among women with a high intake (as measured by excretion) of phyto-oestrogens-particularly the isoflavonic phyto-oestrogen equol and the lignan enterolactone. These findings could be important in the prevention of breast cancer.

Effects of diet supplementation with wheat bran on serum estrogen levels in the follicular and luteal phases of the menstrual cycle

There is both epidemiologic and experimental support for the hypothesis that a high-fiber diet can reduce breast cancer risk; this may be due, at least in part, to a reduction in circulating estrogens. This study examined the effects of three levels of wheat bran supplementation (5, 10, and 20 g/d for 2 mo) on the major serum estrogens during both the luteal and follicular phases of the menstrual cycle. The 10- and 20-g supplements, which increased the total dietary fiber intakes to approximately 20 and 32 g/d, respectively, resulted in significant decreases in the luteal serum estrone (P < 0.05 and < 0.02, respectively). The serum estradiol was significantly reduced in the 10-g wheat bran group after 2 mo (P < 0.05); the 20-g supplemented group showed a significant decrease in estradiol at 1 mo (P < 0.02), but not at 2 mo. No changes occurred in the estrone sulfate concentrations. During the follicular phase, the 10-g wheat bran group exhibited a significant reduction in the serum estrone (P < 0.02). Only the serum estrone sulfate showed any reduction with the 20-g supplement, and this just failed to achieve significance (P = 0.07). Serum sex hormone-binding globulin levels were unaffected by wheat bran. When of long duration, these effects may be sufficient to favorably influence breast cancer risk in Western women.

Eating to beat breast cancer: potential role for soy supplements

BACKGROUND

The study reviews the anticancer properties of natural isoflavones which occur in especially high concentration in soybeans. It considers the suitability of soybean products for clinical trials aiming to reduce the progression of breast cancer.

METHODS

Evidence is reviewed that plant isoflavones such as genistein show cytostatic activity against human mammary cancer cell lines in vitro and can also suppress carcinogen-induced mammary cancer in young and mature rats.

RESULTS

Plant isoflavones are converted in the bowel to compounds with potential antioestrogenic and antioxidative properties. These compounds show cytostatic activity for both oestrogen receptor-positive and negative human mammary cancer cell lines, and also inhibit growth and progress of the rat mammary cancer model. The high content of soybean products in the diet of Asian women has been postulated as one reason for their relatively low breast cancer incidence.

CONCLUSION

Preclinical studies suggest that soybean products be given priority for clinical trials in breast cancer protection. A pilot study could test soy protein supplements as long-term adjuvant dietary treatment after primary surgery for early breast cancer, looking for a decrease in the risk of recurrence or of second primary tumours.

Vitamins C and E, retinol, beta-carotene and dietary fibre in relation to breast cancer risk: a prospective cohort study

Association between breast cancer risk and the intake of vitamins C and E, retinol, beta (beta)-carotene, dietary fibre, vegetables, fruit and potatoes was examined in The Netherlands Cohort Study, for 62,573 women aged 55-69 years. After 4.3 years of follow-up, 650 incident breast cancer cases were identified. After adjusting for traditional risk factors, breast cancer risk was not influenced by the intake of beta-carotene, vitamin E, dietary fibre, supplements with vitamin C, vegetables or potatoes. Fruit consumption showed a non-significant inverse association with breast cancer risk (RR highest/lowest quintile = 0.76, 95% CI 0.54-1.08). A small reduction in risk was also observed with increasing intake of dietary vitamin C (RR highest/lowest quintile = 0.77, 95% CI 0.55-1.08). For retinol, a weak positive association was observed (RR highest/lowest quintile = 1.24, 95% CI 0.83-1.83). Among subjects with a high intake of polyunsaturated fatty acids (PUFAs), both beta-carotene and vitamin C intake showed a non-significant inverse association with breast cancer risk (P-trend = 0.15 and 0.16 respectively). Our findings do not suggest a strong role, if any, for intake of vitamins C and E, beta-carotene, retinol, dietary fibre, vegetables, fruit and potatoes in the aetiology of breast cancer.

Dietary fiber and risk of breast cancer: a case-control study in Uruguay

To examine whether dietary fiber modifies breast cancer risk, a case-control study involving 351 newly diagnosed patients with breast cancer and 356 hospitalized controls was conducted in Uruguay. Dietary patterns were assessed in detail by use of a food frequency questionnaire on 64 items, which allowed the calculation of total energy intake. Nutrient residuals were calculated through regression analysis. After adjustment for potential confounders (which included age, residence, family history of breast cancer, prior history of benign breast disease, parity, total energy, red meat, lutein/zeaxanthin and quercetin intake, and menopausal status), dietary fiber and total nonstarch polysaccharides were associated with a strong reduction in risk of breast cancer (odds ratio for uppermost quartile of total dietary fiber = 0.51, 95% confidence limit = 0.31-0.82). Also the dose-response pattern was highly significant (p < 0.001). The inverse association was observed in pre- and post-menopausal women and was similar for soluble and insoluble fiber. Furthermore, dietary fiber displayed a strong joint effect with fat, quercetin, and lutein/zeaxanthin.

Vitamin E concentration in breast adipose tissue of breast cancer patients (Kuopio, Finland)

Previous data on animals and humans suggest that vitamin E may be a protective factor against cancer. A low dietary vitamin E intake has been suggested to increase the risk of breast cancer. We examined the dietary intake and the concentration of vitamin E in breast adipose tissue of women in Kuopio, Finland, diagnosed between 1990 and 1992 with benign breast disease (n = 34) and with breast cancer (n = 32). In postmenopausal women, lower dietary intake (P = 0.006) and a smaller concentration of vitamin E in breast adipose tissue (P = 0.024) were observed in breast cancer patients than in subjects with benign breast disease. Partial correlation showed that the vitamin E concentration in the breast adipose tissue correlated positively with the dietary intake of vitamin E (r = 0.25, P = 0.023), indicating that the vitamin E concentration in breast adipose tissue reflects the dietary intake of vitamin E.

Repeated immunotherapy using intratumoural injection with recombinant interleukin-2 and tumour-infiltrating lymphocytes inhibits growth of breast cancer and induces apoptosis of tumour cells

This study tested the effect of repeated intratumoural injection with recombinant interleukin-2 (rIL-2) and tumour-infiltrating lymphocytes (TILs) on inhibition of growth of breast cancer and on induction of apoptosis of tumour cells. The tumour cell line LDLX43 was used to induce breast cancer in Wistar rats. Group I (10 rats) was the control. Group II (12 rats) received repeated intratumoural injection with rIL-2 and TILs. rIL-2 at the dose of 5 x 10(5) IU/day was given for 7 days, and 1 x 10(7) TILs were injected on the second day of each rIL-2 therapy, for a treatment session. Overall, two treatment sessions of immunotherapy with rIL-2 and TILs were given in all treated animals. Rapid increased tumour volume was found in the control group. In the treated group the total response rate was 42%, of which 25% tumours showed partial regression and 17% tumours reached complete remission where infiltration of plenty of T lymphocytes was detected, indicating that T cell-mediated antitumour immunity is primarily responsible for tumour rejection. Further investigation showed the repeated immunotherapy using intratumoural injection with rIL-2 and TILs could induce the development of apoptosis of breast cancer cells.

Can supplementary dietary fibre suppress breast cancer growth?

Case-control studies in diverse populations around the world have reported a lower risk of breast cancer in association with higher intake of dietary fibre and complex carbohydrates. Although this has not been confirmed in prospective studies in the USA, the observations have prompted the hypothesis that prolonged use of dietary fibre supplements might reduce breast cancer risk in high-incidence populations. Several possible mechanisms of action have been suggested, all involving a reduction of bioactive oestrogen levels in the blood. The various mechanisms are not necessarily mutually exclusive. First, a high-fibre diet might reduce circulating oestrogen levels by reducing the enterohepatic recirculation of oestrogen. Second, many plants and vegetables contain isoflavones and lignans capable of conversion in the bowel into weak oestrogens that may compete with oestradiol for target binding-sites. Third, a high-fibre diet is less often associated with obesity, which tends to increase availability of the biologically active 16-alpha metabolites of oestrone. Fourth, a high-fibre diet usually has a lower content of fat and a higher content of antioxidant vitamins, which may protect against breast cancer risk. Finally, diets rich in fibre and complex carbohydrates have been shown to improve insulin sensitivity, with an associated reduction in circulating oestrogen levels. Synergism between these effects offers a possible mechanism by which a high fibre intake might suppress breast cancer growth in women.

Cohort studies of fat intake and the risk of breast cancer--a pooled analysis

BACKGROUND

Experiments in animals, international correlation comparisons, and case-control studies support an association between dietary fat intake and the incidence of breast cancer. Most cohort studies do not corroborate the association, but they have been criticized for involving small numbers of cases, homogeneous fat intake, and measurement errors in estimates of fat intake.

METHODS

We identified seven prospective studies in four countries that met specific criteria and analyzed the primary data in a standardized manner. Pooled estimates of the relation of fat intake to the risk of breast cancer were calculated, and data from study-specific validation studies were used to adjust the results for measurement error.

RESULTS

Information about 4980 cases from studies including 337,819 women was available. When women in the highest quintile of energy-adjusted total fat intake were compared with women in the lowest quintile, the multivariate pooled relative risk of breast cancer was 1.05 (95 percent confidence interval, 0.94 to 1.16). Relative risks for saturated, monounsaturated, and polyunsaturated fat and for cholesterol, considered individually, were also close to unity. There was little overall association between the percentage of energy intake from fat and the risk of breast cancer, even among women whose energy intake from fat was less than 20 percent. Correcting for error in the measurement of nutrient intake did not materially alter these findings.

CONCLUSIONS

We found no evidence of a positive association between total dietary fat intake and the risk of breast cancer. There was no reduction in risk even among women whose energy intake from fat was less than 20 percent of total energy intake. In the context of the Western lifestyle, lowering the total intake of fat in midlife is unlikely to reduce the risk of breast cancer substantially.

Nutrition and breast cancer

Epidemiologic evidence on the relation between nutrition and breast cancer is reviewed. After several decades of study, many aspects of the role of diet in breast cancer etiology are still unclear. Results from large prospective studies do not support the concept developed from animal and ecologic evidence that dietary fat intake in mid-life is associated with breast cancer risk. Thus, if fat intake is relevant to breast cancer, it is probably only at extremely low fat intakes or during early life. An emerging hypothesis that higher energy intake and growth rate in childhood and adolescence increases risk deserves further study. The possibility that diets rich in olive oil may be protective is also intriguing. Considerable evidence suggests that low intake of vegetables modestly increases the risk of breast cancer; however, the nutrients responsible remain elusive. The positive relation of alcohol intake with breast cancer risk has been seen repeatedly, and recently has been buttressed by studies showing that moderate alcohol intake increases estrogen endogenous levels. Advice to increase vegetable intake and limit alcohol consumption would probably have a modest, at best, effect on breast cancer risk. Future studies of the relation of nutrition during early life to subsequent breast cancer risk are needed.