Differentiation of the mammary gland and susceptibility to carcinogenesis

Ethanol consumption and DMBA-induced mammary carcinogenesis in rats

In this study, we report that chronic ethanol intake at 20% of calories can enhance the initiation stage and at 15% of calories can enhance the promotion stage of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumorigenesis in female Sprague-Dawley rats. Ethanol consumption at 20% of calories by female rats from 25 to 53 days of age was associated with a significant increase in terminal end bud (TEB) structures and a significant decrease in alveolar bud structures of the normal mammary gland. In addition to changes in mammary gland morphology, ethanol consumption at 20% of calories also was associated with a significant increase in incorporation of [3H]thymidine into mammary DNA and a significant increase in the DNA-labeling index of mammary TEB. Therefore, specific ethanol intakes can enhance DMBA-induced mammary tumorigenesis. The enhancement of the initiation stage partly may be explained by alterations in the structural development of the normal rat mammary gland that increase susceptibility to chemically induced mammary tumorigenesis.

Endocrine aspects of cancer: an epidemiological approach

Over the last 2 decades epidemiologists have increasingly used parameters of endocrine function in their studies. Prospective cohort studies offer methodological advantages in view of the latency between the relevant hormonal exposure and the clinical onset of cancer. Examples from the author's experience are provided. Evidence is mounted for an important "time window" for breast cancer development between menarche and the birth of a first child.

Relationship of growth factors and differentiation in normal and neoplastic development of the mammary gland

The different mammary cell lines described herein appear to be representative of the cell types found in both normal glands and benign tumors of rats and humans. The epithelial cell lines can differentiate to both alveolar-like and myoepithelial-like cells in culture. The epithelial cell lines and particularly those cell lines representing intermediate stages in the myoepithelial differentiation pathway are candidates for the epithelial stem cells found in rat and possibly in human terminal ductal structures. The systemic mammatrophic hormones that are thought to control the growth of the mammary gland in vivo have little or no stimulatory effect alone on the growth of normal and neoplastic rat mammary cells in culture. The pituitary growth factors (fibroblast growth factor [FGF] and pituitary-derived mammary growth factor [PMGF],) and the growth factors released from the different cell lines, (stromal prostaglandin E2 [PGE2] and myoepithelial transforming growth factor alpha [TGF-alpha]) are much more potent mitogenic agents for the mammary cell lines. The ability of FGF and epidermal growth factor (EGF) -related molecules to simulate growth of the different mammary cell types in culture correlates with the presence of their high-affinity receptors. Thus these growth factors are promising candidates for some of the primary effectors of mammary growth in vivo. Malignant mammary epithelial cells have a greatly reduced rate of growth compared to their normal and benign counterparts. They also fail to differentiate or to respond to PMGF but can still respond to PGE2 and TGF-alpha. In addition, highly malignant variants appear capable of adapting to a new growth environment in vivo. This suggests that simple molecular explanations based solely on the autostimulation of cell growth may not be sufficient to explain some of the properties of the slowly growing, highly malignant cells.

Hormone dependence of a mouse mammary tumor line induced in vivo by medroxyprogesterone acetate

The administration of MPA to virgin female BALB/c mice led to the development of mammary adenocarcinomas, which in further in vivo transplants gave rise to both MPA-dependent and MPA-independent lines. In this paper we chose one of the MPA-dependent lines with high contents of estrogen (ER) and progesterone (PR) receptors, and were able to demonstrate that a) the growth of these tumors could be manipulated by the administration or the withdrawal of the hormonal supply; b) PR were down-regulated in MPA-treated mice; c) progesterone had the same stimulatory effect as MPA on tumor growth; d) tumors did not grow in estrogen-treated mice; e) tumor growth was much lower in males than in females; f) the presence of the ovaries had a positive influence on tumor growth, even in the presence of MPA; g) the withdrawal of progestin pellets in ovariectomized mice usually led to complete remissions followed by regrowth of the tumors after several weeks; and h) the regrowing tumors maintained their steroid receptor pattern and (in 3 out of 4 cases) their hormone-dependent behavior in further passages.

Epidemiology and natural history of breast cancer. Implications for the body weight-breast cancer controversy

The mechanisms of differentiation of the mammary gland apparently can explain the contradictory findings on the association of breast cancer with excess body weight. Excess weight may be related to the initiation of breast cancer in premenopausal women through its effect on menstrual cycles and on progesterone secretion and to the promotion of breast cancer in postmenopausal women through its effect on estrogen metabolism. Although body weight is unlikely to be as strong a risk factor for breast cancer as it is for endometrial cancer, it may have a greater importance from a public health point of view, because the ratio of the incidence of breast cancer to that of endometrial cancer is 4.5 in whites and 6 in blacks. Thus, more studies seem warranted. It is not possible, however, to rule out the view that the reported correlation between excess weight and breast cancer is attributable to failure to adjust for potential confounders, such as dietary fat. New insights may come from the combined assessment of weight, different types of dietary fat, and reproductive history factors known to be involved in the natural history of breast cancer. For example, in the Women's Intervention Nutrition Study (WINS), the survival rate of breast cancer patients on a 20 per cent fat diet is being compared with that of breast cancer patients of similar weight keeping their usual 35 to 40 per cent fat diet. This investigation will show whether dietary fat influences the rate of progression (metastasis) and of promotion (occurrence of cancer in the other breast) independent of body weight.

Protective effect of chorionic gonadotropin on DMBA-induced mammary carcinogenesis

The effect of the placental hormone chorionic gonadotropin (hCG) on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumours was studied in young virgin Sprague-Dawley rats. This hormone when administered at a dose of 100 IU day-1 does not induce toxic effects, measured as alterations in body weight or weight of endocrine organs, and has a reversible effect on oestrous cycle. The lack of toxicity and the fact that hCG treatment terminated prior to administration of the chemical carcinogen DMBA protects the mammary gland from malignant transformation, led us to test the effect of hCG treatment on DMBA-initiated mammary tumours. Fifty day-old virgin Sprague-Dawley rats received intragastrically 8 mg DMBA per 100 g body weight and were divided into two groups: group I animals were treated with DMBA only and group II received DMBA at age 50 and in addition, a daily intraperitoneal injection of 100 IU hCG for days 21-81 post carcinogen administration. Tumorigenic response was evaluated by biweekly palpation of all animals and by complete autopsy 24 weeks after DMBA treatment. Group I animals developed an incidence of 100% of both tumours and adenocarcinomas. Group II animals developed a significantly lower incidence of tumours and adenocarcinomas, 51.5% and 45.5% respectively. In both groups lesions developed more frequently in thoracic than in abdominal mammary glands. It is postulated that hCG treatment, probably through stimulation of ovarian oestrogen and progesterone synthesis, induces differentiation of mammary epithelium that although affected by the carcinogen can still be rescued from malignant transformation.

Alcohol consumption and breast cancer

Epidemiologic studies of the relationship of alcohol consumption and breast cancer are generally in support of a direct association, although they are not entirely consistent. Studies supporting this finding have come from many countries around the world and from many investigators working with different study designs and types of populations. Ten of 16 case-control studies, and five of six cohort studies have produced results supporting a positive association. When evaluated together through techniques such as meta-analysis, these studies suggest that there is a 50% increase in breast cancer risk for women who average between one and two drinks per day. All types of alcoholic beverages seem to increase the risk, but there is little agreement between studies on dose-response relationships. No biologic explanation for alcohol's possible role in breast carcinogenesis is yet known, but several hypotheses have been advanced. In the absence of any effective method of primary breast cancer prevention, and because current risk factors explain so little of the incidence of this common cancer, alcohol consumption is of potential importance from both public health and etiologic perspectives. The possible protective effect of moderate alcohol consumption on heart disease should be considered when assessing the risks of this level of consumption on breast cancer.

Approaches to breast cancer prevention

It may be possible to delay the step-by-step progression towards frank invasive cancer by avoiding one or more of the well-known clinical risk factors. In addition current clinical trials in the USA and Europe are assessing whether the use of tamoxifen, vitamin analogues or a low-fat diet can delay the appearance of overt disease in women known to be at high risk, but it will be several years before such trials can be evaluated. For women seeking advice on prevention, non-toxic supplements to the diet such as beta-carotene, vitamin A analogues or selenium compounds, and the avoidance of alcohol and obesity, are examples of practical advice which can do no harm yet may help to protect against breast cancer development. In the case of the very anxious first degree relative of a breast cancer patient, the current choice lies essentially between regular monitoring, mastectomy with reconstruction, early termination of ovarian activity and anti-oestrogen therapy. Currently, considerable research is being directed towards identifying oncogenes and growth factors which are involved in the growth of breast cancer. In the meantime, more research needs to be devoted to the effect of various progestagens in counteracting oestrogen support of breast cancer growth, and to biological observations on different formulations and doses of combined oestrogen/progestagen preparations which may reduce breast cancer risk both in pre- and postmenopausal women.

Risk of cancer of the breast after legal abortion during first trimester: a Swedish register study

An increase in induced abortions in Sweden has been accompanied by an increase in the incidence of breast cancer of about 40% in women aged 20-44. To assess whether the apparent risk is real the risk of breast cancer was investigated in practically all Swedish women with a history of a legal abortion in the first trimester before the age of 30 during 1966-74 (n = 49,000). The cohort was followed up in the Swedish cancer register to identify cases of breast cancer diagnosed more than five years after the abortion until the end of 1984. The number of observed cases of breast cancer was 65 compared with an expected number of 84.5, estimated from the contemporary Swedish population with due consideration to age, giving a relative risk of 0.8 (95% confidence interval 0.58 to 0.99). Contrary to most earlier reports, this study did not indicate any overall increased risk of breast cancer after an induced abortion in the first trimester in young women.

Hormone prevention of mammary carcinogenesis by norethynodrel-mestranol

The observation that the susceptibility of the mammary gland to chemical carcinogenesis is inversely related to its level of hormonally induced differentiation led us to test whether treatment of virgin rats with an estrogenic-progestagenic hormone combination protected the gland against this carcinogenesis. Virgin Sprague-Dawley rats aged 45, 55, 65, or 75 days had implanted subcutaneously for 21 days a pellet containing norethynodrel-mestranol (NM) (98.5%-1.5%) at two doses, a physiological or low dose (LD) of 0.5 mg, equivalent to the dose used in Enovid for contraception in humans, and a pharmacological or high dose (HD) of 5.0 mg. Twenty-one days after NM pellet removal, the mammary glands of 5 animals per group were examined for the number of terminal end buds (TEBs), terminal ducts (TDs), alveolar buds (ABs) and lobules, and the DNA labeling index (DNA-LI). The remaining animals received 8 mg 7,12-dimethylbenz(a) anthracene (DMBA)/100 g body weight, and tumorigenesis was evaluated at 24 weeks. The percentage of TEBs decreased with age, and further with NM treatment at both doses. Treatment did not significantly modify the percentage of TDs, but increased that of ABs in most groups. The DNA-LI of TEBs remained constant, even during aging and after treatment, whereas both aging and treatment reduced DNA-LI in TDs and ABs. Tumor incidence declined with increasing age from 75% to 44% in the 45 and 75 day-old control groups respectively. Adenocarcinoma incidence followed the same trend. NM treatment had a dose-related protective effect against development of tumors in general and of adenocarcinomas in particular. LD treatment resulted in a marginally significant reduction in adenocarcinoma incidence, whereas HD-treated animals were 0.24 times as likely as controls to develop carcinomas. There was a statistically significant correlation between the percentage of TEBs present in the gland at the time of carcinogen administration and the incidence of adenocarcinomas. It was concluded that treatment of virgin rats with the hormone combination norethynodrel-mestranol resulted in long lasting structural changes in the mammary gland which protected this organ from a subsequent carcinogenic insult.

Heritability of breast cancer and its role in pre-menopausal cases

The causes for the pre-menopausal incidence peak in breast cancer are still controversial. Other cancers also show an early incidence peak. Since the mammary tissue only starts to develop in puberty, the pre-menopausal incidence peak for breast cancer is comparable to the 'juvenile' peak in other cancers (retina, kidney). The four-mutation model for oncogenesis can explain pre-menopausal breast cancer. The model suggests that malignant transformation of a cell is due to four specific oncogenic mutations. These specific mutations accumulate during the proliferation of somatic cells. According to the model, one inherited oncogenic mutation can cause hereditary cancer. In this case only three additional specific mutations have to be accumulated during somatic cell proliferation. Epidemiological data and mathematical calculations indicate that in this case tumors occur early in life. Thus, the four-mutation model for oncogenesis predicts that the impact of heritability in pre-menopausal breast cancer is more significant than is generally believed. At this point, molecular biological studies are needed, to identify the involved specific mutations. Other implications of the model are an increased incidence of second primary tumors and an increased sensitivity for mutagenic factors in these patients.

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.

Effects of age on multiple organ carcinogenesis induced by 3,2'-dimethyl-4-aminobiphenyl in rats, with particular reference to the prostate

The effects of age on multi-organ carcinogenesis induced by 3,2'-dimethyl-4-aminobiphenyl (DMAB) in male F344 rats were examined. Groups of 5-, 35-, and 65-week-old animals were given 4 weekly sc injections of DMAB at a dose of 200 or 150 mg/kg body weight. Prostate carcinomas were induced in 8 to 19% of rats treated, no significant differences in the incidence between different ages being observed. Tumors in the small intestine, skin, pancreas and peritoneum, however, developed more frequently in young than in old animals, whereas higher incidences of testis, preputial and mammary gland lesions were found in the 35- and/or 65-week-old groups. Colon and Zymbal gland carcinogenesis did not reveal any age dependence.

The search for the causes of breast and colon cancer

Epidemiological studies of breast and colon cancers implicate diet as a causative factor but the evidence is stronger for colon cancer, the occurrence of which may be reduced by diets with less animal fat and more fruit and vegetables.

Reproductive events, occurring in adolescence at the time of development of reproductive organs and at the time of tumour initiation, have a bearing on growth characteristics and reproductive hormone regulation in normal and tumour tissue investigated decades later--a hypothesis

Both animal and human data indicate that reproductive events taking place early in reproductive life may have an important influence on growth characteristics and reproductive hormone regulation in both normal tissue and neoplastic tissue investigated later in life.

Effect of medroxyprogesterone acetate on the response of the rat mammary gland to carcinogenesis

In order to determine whether mammary gland differentiation, which is known to protect this organ from chemically induced carcinogenesis, can be stimulated in virgin rats by administration of a progestagenic agent, medroxyprogesterone acetate (MPA) was given to 300 Sprague-Dawley virgin rats, which at the ages of 45, 55, 65 and 75 days, groups I, II, III and IV respectively, had implanted an MPA pellet of 0.5 mg (low dose-LD) or 5.0 mg (high dose-HD). Pellets were removed after 21 days, and 21 days later five animals per group were killed for evaluation of mammary gland development. The remaining animals received 8 mg 7,12-dimethylbenz(a)-anthracene (DMBA) per 100 g body weight, and were killed after 24 weeks for evaluation of tumour incidence. Both age and treatment affected mammary gland structure and had a significant interaction in the proportion of terminal end buds (TEBs) present. The number of TEBs decreased as a function of age; treatment at both LD and HD did not modify the proportion of TEBs in groups I and III; LD decreased their percentage in group II, and both doses markedly increased TEB percentage in group IV animals. MPA LD treatment did not affect overall tumour and adenocarcinoma incidence although group IV animals developed greater incidences than their respective controls. MPA HD treated rats were 2.45 times more likely to develop tumours than their respective controls. Adenocarcinoma incidence had a significant positive correlation with the percentage of TEBs present. It was concluded that this progestagenic agent did not increase the risk of carcinoma development when administered to virgin rats at the clinical dose used for contraception. However, a 10-fold dose increase resulted in a higher tumorigenic response.

Toxicity and carcinogenicity of nitrofurazone in F344/N rats and B6C3F1 mice

Toxicology and carcinogenesis studies were conducted by feeding diets containing nitrofurazone (99% pure) to groups of F344/N rats and B6C3F1 mice for 14 days, 13 wk or 2 yr. In the 14-day studies, in which doses ranged from 630 to 10,000 ppm, nitrofurazone was more toxic to mice than to rats. Accordingly, in the 13-wk studies, doses for rats ranged from 150 to 2500 ppm and for mice from 70 to 1250 ppm. At the higher doses, convulsive seizures and gonadal hypoplasia were observed in both species. Evidence of toxicity in rats also included degenerative arthropathy. For the 2-yr studies, rats were exposed to 0, 310 or 620 ppm nitrofurazone and the survival of male rats given 620 ppm was lower than that of controls (33/50, 30/50 and 20/50 in the control, 310- and 620-ppm groups, respectively). Nitrofurazone administration increased the incidences of mammary gland fibroadenomas in female rats (8/49, 36/50 and 36/50 in the control, 310- and 620-ppm groups, respectively). In male rats it was associated with a marginal increase in sebaceous gland adenomas and trichoepitheliomas of the skin, mesotheliomas of the tunica vaginalis, and tumours of the perputial gland. Nitrofurazone caused testicular degeneration (atrophy of germinal epithelium and aspermatogenesis) in rats, and degeneration of vertebral and knee articular cartilage in rats of both sexes. In mice, dietary concentrations of nitrofurazone for the 2-yr studies were 0, 150 or 310 ppm. In mice of each sex, nitrofurazone administration induced stimulus-sensitive convulsive seizures, primarily during the first year of study. In male mice, there was no evidence of any chemically-related carcinogenic effects, but there was a treatment-related decrease in survival (39/50, 31/50 and 27/50 in the control, 150- and 310-ppm groups, respectively). In female mice nitrofurazone induced ovarian lesions with increased incidences of benign mixed tumours (0/47, 17/50 and 20/50 in control, low- and high-dose groups, respectively) and granulosa cell tumours (1/47, 4/50 and 9/50 in control, low- and high-dose groups, respectively).

Oral contraceptives and breast cancer. A review

Case-control and cohort studies published between 1977 and 1988 were reviewed with the purpose to evaluate the relationship between use of oral contraceptives (OC-use) and breast cancer risk, tumour biology and tumour prognosis with special emphasis on early OC-use. The risk of breast cancer was assessed in 30 case-referent studies and 5 cohort studies, and the prognosis of breast cancer had been studied in 9 reports. Definition of OC-use, prevalence of OC-use, latency time between start of OC-use and tumour diagnosis, case identification and choice of referents, study size, study quality were assessed. The outcome of the studies is presented. From the results of the analyses the author concludes that there is no overall risk for breast cancer among OC-users. However, with the emphasis on early OC-use, consistent results seem to emerge showing an increased risk of premenopausal breast cancer, when the possible bias of different latency times is taken into account. Also results on breast cancer incidence in early exposed age groups, tumour biology and prognosis in early OC-users with breast cancer support a genuine risk relationship. The effects of different OC-brands and dose, and the risk of peri- and postmenopausal breast cancer after early OC-use can at present not be assessed.

Short term increase in risk of breast cancer after full term pregnancy

To determine whether there is a short term increase in the risk of breast cancer after a full term birth data from two hospital based, case-control studies in Italy were pooled. Analysis was restricted to women aged under 50 with two or more children (573 women with cancer and 570 controls). A relative risk for breast cancer of 2.66 was seen in women who had given birth during the three years preceding the interview compared with women whose last birth had occurred 10 or more years before, after adjustment for age, age at first birth, and parity. The relative risk slowly decreased for women who had last given birth three to 10 years before. Multivariate analyses confirmed the protective effect of an early age at first birth and the age dependent effect of parity on the risk of breast cancer--that is, a direct relation below age 40 and an inverse one in older women. These data provide epidemiological evidence that a full term birth is followed by a transient increase in the risk of breast cancer, which for some time contrasts with and overcomes the long term protection of pregnancy at an early age. They therefore confirm predictions from animal studies and theoretical models that pregnancy prevents the early stages of breast carcinogenesis but promotes the late stages of the process.

The effect of age and menstrual cycle upon proliferative activity of the normal human breast

The aim of this study was to determine the proliferative activity within the epithelial cells of the normal human breast in 122 patients (6 reduction mammoplasties and 116 fibroadenoma excisions) in relation to age and the phase of the menstrual cycle. Thirty three of the patients were on oral contraceptives and 33 were parous. Thin tissue slices were incubated with tritiated thymidine and processed for autoradiography. Other samples were fixed directly and prepared for histology. The labelling, mitotic and apoptotic indices (LI, MI and AI) were determined and all illustrated considerable variability. The labelling indices are significantly (P less than 0.05) influenced by both patient age and stage during the menstrual cycle and ranged from 0-11.5%. Maximum LI values were obtained on the 20.8th day of the cycle. A square root transformation of the data was used to reduce the skewness of the data to a more normal distribution. The square root of the LI declined by 0.22 per decade. The mitotic data showed similar significant (P less than 0.05) correlations against age and day of cycle with a peak on the 21.5th day of the cycle, a decline by 0.072 per decade and a range from 0-0.6%. The data for apoptotic cells were less clearly influenced by the stage of the menstrual cycle but showed a significant (P less than 0.5) decline with age. The AI in parous patients was significantly higher than that in non-parous patients. There was no significant effect of oral contraceptives on any of the parameters measured when age and stage of cycle were taken into account. The considerable variability in the data could not be fully accounted for by either technical factors, the age of the patients, or the day of the cycle. We conclude that proliferation is negatively related to age and is influenced by the menstrual cycle but that additional as yet unknown factors must account for a large part of the variability seen in the data.

A unifying concept of the aetiology of breast cancer

A number of risk factors for breast cancer are considered jointly in one pathogenetic framework which relates to the formation of pre-cancerous lesions. Energy-rich diet during puberty and adolescence enhances the occurrence of pre-cancerous lesions in the breast. This process is counteracted by full-term pregnancies, and the earlier they come the fewer the number of such lesions. Energy-rich diet later in life contributes to the occurrence of obesity which, after menopause, enhances the growth of existing subclinical and clinical breast cancer. In both periods of life the nutritional factor exerts its effect through endocrine mechanisms in which oestrogens play a major part.

Independent molecular pathways in initiation and loss of hormone responsiveness of breast carcinomas

These studies were set up to determine whether those oncogenes participating in the initiation of mammary carcinogenesis (for example, ras oncogenes) play a direct role in the outcome of events associated with the late stages of tumor development such as loss of hormone dependency. Mammary carcinomas induced by a single carcinogenic insult in pubescent rats was selected as an in vivo model system with direct relevance to human breast cancer. Acquisition of hormone-independent growth in these carcinogen-induced tumors was found to be independent of the activation of ras oncogenes during the early stages of carcinogenesis. In agreement with these observations, introduction of a human ras oncogene into human MCF-7 breast carcinoma cells did not abrogate their hormonal dependency for growth in vivo. These findings suggest that those events responsible for the critical stages of breast cancer development occur independently and in an uncoordinated manner.

The role of oestrogens and progestagens in the epidemiology and prevention of breast cancer

The protective effect of early menopause shows that ovarian hormones increase the risk of breast cancer: it is likely that this is because they stimulate breast cell division. The mitotic rate of breast cells is higher during the luteal phase of the menstrual cycle than during the follicular phase, suggesting either that progesterone and oestrogen together induce more mitoses than oestrogen alone (the 'oestrogen plus progestagen hypothesis') or that oestrogen alone induces breast cell mitoses in a dose-dependent manner and that progesterone has no effect (the 'oestrogen alone hypothesis'). Both hypotheses are consistent with the known effects of reproductive history, obesity, combined oral contraceptives and oestrogen replacement therapy (ERT) on breast cancer risk, but while the oestrogen alone hypothesis predicts that hormone replacement therapy with oestrogen and a progestagen (HRT) will cause the same increase in risk as ERT, the oestrogen plus progestagen hypothesis predicts that HRT will cause a greater increase in risk than ERT. Both hypotheses suggest that the risk of breast cancer could be reduced by delaying the onset of regular ovulatory menstrual cycles and by minimizing the therapeutic use of oestrogens, and possibly of progestagens, in postmenopausal women. It may be possible to design hormonal contraceptives that will decrease breast cancer risk.

Effects of dietary fat on long-term growth and mammary tumorigenesis in female Sprague-Dawley rats given a low dose of DMBA

The effects of dietary fat on experimental mammary cancer have typically been observed in relatively young animals. However, in human populations, breast cancer incidence and mortality are highest in postmenopausal women. To develop an animal model that stimulates the human situation more closely, female Sprague-Dawley rats were given a relatively small dose (1.5 mg) of 7,12-dimethylbenz[a]anthracene (DMBA) at 50 days of age while on a semipurified diet containing 3% sunflower-seed oil. One week later, half of the 70 rats were transferred to a diet containing 20% sunflower-seed oil. Very few mammary lesions appeared until about 35 weeks after administration of DMBA, at which time palpable mammary nodules began to appear in many of the animals on the high-fat diet. More than half of the animals in this group had developed nodules by Week 41, whereas the other half of the animals on the low-fat diet developed nodules by Week 46. Rats on the high-fat diet gradually became much more obese than those on the low-fat diet and were significantly heavier at the time they developed lesions. The incidence of nodules continued to increase in both groups and reached 100% in the group fed the high-fat diet by Week 55, with a 70% incidence of adenocarcinomas. At this time, 79% of the animals on the low-fat diet had palpable nodules without a plateau in incidence being reached. On autopsy, adenocarcinomas were found in 57% of animals on the low-fat diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Human breast epithelial xenografts: an immunocytochemical and ultrastructural study of differentiation and lactogenic response

Fragments of ductal and lobular epithelium ('organoids') produced by collagenase digestion of reduction-mammoplasty specimens were injected into athymic 'nude' mice. These heterospecific tissues were accepted without rejection, and the presence of xenografts was confirmed by cytology, immunocytochemistry and chromatin staining. Lactation, as confirmed by immunocytochemical and ultrastructural criteria, was observed in the grafted human epithelium during murine pregnancy at both intra- and extra-mammary sites.

On the mechanisms relevant to nutritional carcinogenesis

Prevention of the nutritionally linked cancers will be on a sounder footing eventually if the measures recommended not only are consonant with international epidemiological data and the results of laboratory experimentation, but also rest on an understanding of the mechanisms of action of the various nutritional factors. The process of cancer causation involves a series of steps that can be classified broadly into (a) the definition of DNA-reactive carcinogens and (b) the assessment of enhancing or inhibiting epigenetic agents. For cancers highly prevalent in the Western world, especially of the breast, colon, and pancreas, and perhaps also of the prostate, evidence has begun to accrue that a new type of heterocyclic amine formed during cooking of meat or fish constitutes the DNA-reactive carcinogen. The type and amount of fat play a role in enhancing the effect of epigenetic mechanisms that characteristically are highly sensitive to dosage and duration. These epigenetic phenomena are also reversible. Cereal fiber, by increasing stool bulk, dilutes epigenetic promoters in the intestinal tract. Therefore, based on mechanistic understanding, reduction in risk is feasible by lowering fat, increasing fiber, and perhaps by altering cooking modes.

Stem cells and the development of mammary cancers in experimental rats and in humans

Evidence based on immunocytochemical staining and ultrastructure suggests that morphological gradations between epithelial and myoepithelial cells, and possibly between epithelial cells and alveolar-like cells occur in terminal ductal structures of rat and human mammary glands. The benign carcinogen-induced rat and benign human mammary tumors can contain epithelial, myoepithelial-like and alveolar-like cells, whereas the malignant counterparts mainly contain only epithelial-like cells. Clonal epithelial cell lines from normal rat mammary glands, benign tumors, and SV40-transformed human mammary glands can differentiate to either myoepithelial-like or alveolar-like cells. In those of the rat, the differentiation processes occur in steps: intermediate cells along the myoepithelial-like pathway resemble intermediates in terminal ductal structures in vivo, and can also generate certain well-differentiated mesenchymal elements of the original tumours. Differentiation of the benign rat cells to alveolar-like cells with mammatrophic hormones and retinoids in vitro leads to a reduction in their tumor-forming ability in vivo. Cell lines from malignant rat mammary tumors of increasing metastatic potential and from human ductal carcinomas largely fail to yield myoepithelial-like or alveolar-like cells and are relatively slow-growing. Growth of the rat mammary epithelial cells in culture is stimulated by a pituitary-derived mammatrophic growth factor (PMGF), prostaglandin E2, and alpha-transforming growth factor; the response of the malignant cell lines to PMGF is reduced. It is suggested that stem cells exist in the rat and human glands that are capable of differentiating to the other major cell types of the mammary parenchyma, and that during the carcinogenic process they generate genetically unstable cells which lose their ability to differentiate and attempt to maximise their intrinsically slow growth rate.

Influence of hormones on DNA synthesis of breast tumors in culture

Tissue culture techniques have been developed for studying the influence of hormones on human breast tissues. The present study demonstrated that estrogen induced a highly significant increase in 3H-thymidine incorporation into DNA and labelling index of ductal epithelium of fibrocystic disease; there was no effect of progesterone, either alone or in combination with ovine prolactin, on benign lesions. Estrogen stimulated certain malignant tumors derived from postmenopausal women. These studies also showed that there was an inhibitory effect of 3H-thymidine incorporation into DNA by the effect of progesterone on malignant lesions. When menopausal status was considered, it was found that DNA synthesis was significantly higher in the presence of insulin and hydrocortisone in malignant tumors derived from premenopausal women than from postmenopausal women, or than in benign lesions. Thus, the present findings may provide evidence that specific activity may be an important measurement for breast tumor DNA synthesis in response to ovarian hormones or other substances.

Breast Cancer Risk Factors in Italian Women: A Multicentric Case-Control Study

To evaluate the importance of several risk factors for breast cancer in the Italian female population, a large multicentric case-control study was conducted in 10 breast clinics in Italy. The study included 1,556 women affected by breast cancer, histologically and/or cytologically confirmed. Controls were 1,505 women admitted to a hospital in the same town, matched with cases for residence and with the same age distribution of the Italian female population. The risk factors considered in this study were family history of breast cancer, reproductive history, height and weight, use of oral contraceptives, other hormonal therapies and smoking history. The results of this study confirm the significant role of a positive family history of breast cancer (RR = 2.37); the relative risk was even higher when a first-degree relative was affected or the breast cancer was bilateral. The analysis of the reproductive history showed a significant trend of increasing risk with increasing age at first birth and, although less evident, with increasing number of children. Quetelet's index (kg/m–2) was positively correlated with breast cancer risk, mostly in postmenopausal women. Among other studied factors, only late age at menopause confirmed an increased risk for breast cancer, whereas age at menarche, use of oral contraceptives and smoking histories did not show any significant correlation with breast cancer risk. These results are in substantial agreement with other international studies, but represent an interesting contribution to studies about the Italian female population.

Effects of peptides and steroid hormones on cell kinetic parameters of normal human breast tissue in organ culture

Several studies have shown the importance of different hormones in the regulation of mammary tissue growth. The use of organ culture techniques has shown tremendous value for the knowledge of cell proliferation in human breast tissue. Therefore, the purpose of these studies was to analyze the length of the cell cycle, DNA-labeling index, mitotic index, and growth fraction under the effects of insulin, hydrocortisone, and 17-beta estradiol in 5-d organ culture. Normal tissues obtained from patients who underwent breast surgery for benign lesions were individually cultured at 37 degrees C (95% air: 5% CO2 in Medium 199). Autoradiographic studies indicated that the hormones shortened the length of cell cycle of normal breast tissue in 5-d organ cultures. From the growth fraction studies we concluded that the hormones may have stimulated the cells to reenter the cell cycle from Go because these values were increased by the hormones used. Estrogen can alter the S phase duration with a consequent increase in the rate of DNA synthesis which may explain the high DNA-labeling index observed in the present studies.

Isolation and properties of rat cell lines morphologically intermediate between cultured mammary epithelial and myoepithelial-like cells

The cloned cuboidal epithelial cell line Rat Mammary (Rama) 25 converts at low frequency in culture to elongated cells that possess some of the properties of myoepithelial cells; one such clonal cell line is termed Rama 29. Three morphologically intermediate clonal cell lines have been isolated from Rama 25 which form a morphological series in the order: Rama 25 cuboidal cells, Rama 25-Intermediate 2(I2), Rama 25-I1, Rama 25-I4, and Rama 29 elongated cells. This same order is largely maintained for increasing percentages of elongated cells, decreasing percentages of cuboidal cells, decreasing tubular structures on collagen gels, and increasing times of appearance of tumors in nude mice. The fully elongated cells fail to revert to cuboidal cells and to form tumors. Binding of antisera to epithelial-specific milk fat globule membranes and human keratin declines whereas binding of antisera to myoepithelial-associated laminin, vimentin, and Thy-1 increases in the cell lines in the same order. Similarly 7 polypeptides characteristic of elongated cells increase and 4 polypeptides characteristic of cuboidal cells decrease in the cell lines in the same way. Anti-actin serum binds equally to all cell lines grown on plastic, except for Rama 25-I4, where its binding is increased. Rama 25-I1 and Rama 25-I4 cells also give rise to anti-actin, anti-myoglobin, and phosphotungstic acid hematoxylin-staining giant, striated cells on collagen gels and in tumors that also have ultrastructural characteristics of skeletal muscle. Fresh elongated converts of Rama 25 bind appreciably more anti-actin serum than many of the clonal elongated cell lines such as Rama 29. Ultrastructural analysis confirms the gradual loss of epithelial characteristics and the acquisition of immature myoepithelial characteristics in the same sequence of cell lines. It is suggested that such a linear sequence of intermediate morphological states occurs between the Rama 25 cuboidal cells and the elongated myoepithelial-like cells in vitro, and that a similar morphological sequence may exist in terminal ductal structures in vivo.

Mechanisms of selenium inhibition of tumorigenesis

Numerous experiments have demonstrated that selenium supplementation to the diet at modest and nontoxic levels is an effective inhibitor of mammary tumorigenesis in mice and rats. In mice, selenium is most effective during the early stages of tumorigenesis, in particular the events surrounding the induction and expression of the preneoplastic transformation. Whereas selenium is an effective chemopreventive agent, there is little data to support its role as an effective therapeutic agent. The mechanisms of selenium-mediated inhibition of tumorigenesis have not been established. However, the available data suggest that selenium does not act by way of the principal selenoprotein in the cell, glutathione peroxidase, nor does selenium inhibit lipid peroxidation. A number of different mechanisms to explain the inhibitory effects of selenium are discussed; however, definitive answers await further experiments.

Microtubule-disrupting drugs increase the frequency of conversion of a rat mammary epithelial stem cell line to elongated, myoepithelial-like cells in culture

Rat mammary (Rama) 25 cuboidal epithelial stem cells convert at a low frequency to elongated, Thy-1-positive, myoepithelial-like cells in culture; one such cell line is termed Rama 29. Addition of increasing concentrations of the microtubule-disrupting drug colchicine to sparse cultures of Rama 25 dramatically increases the percentage of colonies containing elongated cells and the percentage of Thy-1-positive cells when the drug is removed. Similar results on the formation of elongated cell colonies are obtained with other microtubule disruptors, such as vinblastine, vincristine, demecolcine, and nocodazole. The inactive analogues of colchicine beta- and delta-lumicolchicine and the microfilamental-disruptors cytochalasin B and D are without effect on the formation of elongated cell colonies and Thy-1-positive cells. For a given concentration of colchicine the percentage of elongated cell colonies and Thy-1-positive cells increases the longer the cells are exposed to the drug (range 8-96 hr) and the longer the drug-treated cultures are subsequently grown in drug-free medium. Colchicine fails to display this morphological change on Rama 29 elongated cells and on Rama 600 epithelial cells from a rat mammary metastasizing tumor. Immunofluorescent localization of antisera to tubulin confirms that colchicine disrupts the microtubules in all three cell lines at similar concentrations (0.1 to 1 microM) to those required to increase the percentage of elongated cell colonies in Rama 25. The DNA synthesis inhibitor cytosine arabinoside fails to inhibit this conversion process, and time-lapse cinematographic studies confirm that the conversion of a cuboidal to an elongated cell can take place without cell division. However, cell division may sometimes be required for subsequent stabilization events. Treatment of Rama 25 cells with colchicine under the same conditions also increases the abundance of elongated cell (Rama 29)-associated polypeptides, and elongated cell clones isolated after such treatment show an overall pattern of protein synthesis very similar to that of Rama 29.

Endocrinological studies on breast cancer in the framework of a screening programme

A review is presented of epidemiological investigations carried out since 1974 at Preventicon concerning hormonal aspects of the epidemiology of breast cancer. In addition, some preliminary findings are reported of a study designed to test the hypothesis of luteal insufficiency as a forerunner of cancer of the breast.

Differentiation of mammary epithelial stem cells to alveolar-like cells in culture: cellular pathways and kinetics of the conversion process

The cuboidal epithelial stem cell line Rat Mammary (Rama) 25 can differentiate in culture to droplet, alveolar-like cells that form domes, secrete small amounts of casein, and bind peanut lectin after treatment with neuraminidase. Differentiation to droplet cells is accelerated by dimethyl sulfoxide (DMSO). Morphologically intermediate states (gray and dark) which occur in the order: cuboidal----gray----dark----dark droplet----doming cells have been identified along this pathway by time-lapse cinematography. The dark and dark droplet states are associated with increased peanut lectin binding capacity whereas casein is secreted mainly by cells in domes. Cells in cultures containing low concentrations of DMSO (less than 56 mM) acquire droplets predominantly in the dark state, whereas with higher concentrations of DMSO droplet formation is seen mainly in the gray state. Kinetic analysis both from time-lapse films and conventional microscopy, shows that increasing the concentration of DMSO prolongs the time spent in the gray state, decreases the time of initial appearance of droplet cells, and increases their subsequent rate of formation, without detectable effects on the rates of the remaining morphological transitions. DMSO also reduces the average rate of DNA synthesis and increases the average cell cycle time, particularly in the second (and subsequent) cell cycles after its addition. However, neither droplet nor doming cells are terminally differentiated. Thus a linear sequence of morphological states exists between the Rama 25 stem cells and the alveolar-like or more probably alveolar bud cells in vitro, and DMSO accelerates the overall conversion predominantly by truncating one of the steps in this pathway.

The effect of estrogen, progesterone, thyroxine, and human placental lactogen on DNA synthesis of human breast ductal epithelium maintained in athymic nude mice

Specimens of human breast tissues from the periphery of excised benign tumors, obtained from 17 pre-menopausal patients, were processed into slices and transplanted subcutaneously to 122 female Balb/c athymic nude mice. Subsequently, the host mice were treated with estrogens, progesterone, thyroxine, and human placental lactogen (HPL) alone or in combination. Growth of the ductal epithelium within the human breast transplants, as a function of the hormone treatment, was assessed by 3H-thymidine autoradiographic analysis, i.e., the number of 3H-thymidine radiolabeled ductal cells per unit area of ductal epithelium (labeling index [LI]). The administration of estrogen or thyroxine alone significantly increased the LI. Progesterone or HPL treatments alone did not substantially influence LI. HPL treatment, but not progesterone or thyroxine treatments significantly enhanced the stimulatory effect of estrogen on LI. The athymic nude mouse as host to human breast tissues in these in vivo/ex vivo studies, has been instrumental in producing information that effectively increases understanding of the hormonal factors influencing DNA synthesis in human breast ductal epithelium.

Cellular composition and organization of ductal buds in developing rat mammary glands: evidence for morphological intermediates between epithelial and myoepithelial cells

In the developing rat mammary gland, terminal end buds (TEBs), lateral buds and alveolar buds represent the major sites of morphogenetic activity and cellular differentiation. The morphology and cellular composition of these buds from 20-to 22-day-old rats and cycling rats have been studied by immunocytochemical and electron microscopic techniques. The mammary buds are composed of a heterogeneous collection of cells including epithelial and myoepithelial cells, irregular loosely adherent cells, and occasional large clear cells. The irregular, loosely packed cells or cap cells are mainly situated around the periphery of the TEBs and lateral buds. "Chains" of irregularly shaped cells also extend from the peripheral cap cell layer to the center of the TEB; and, where they converge on lumina, they display microvilli and junctional complexes. At the tips of the end buds, the cap cells are of undifferentiated appearance; however, similar cells situated toward the subtending mammary ducts show a gradation in ultrastructure to that of myoepithelial cells. This change is accompanied by an increase in the amounts of immunoreactive myosin and keratin seen within the cells and a 200-fold increase in the thickness of the basement membrane. In contrast, the peripheral cells of the alveolar buds are more closely packed, contain a greater number of myofilaments, and show increased staining with antisera to myosin. We suggest that the undifferentiated cap cells do not represent a discrete cell type, since they show transitional forms to myoepithelial cells within the subtending mammary ducts, and that the tendency toward the myoepithelial phenotype is predominant in the more differentiated structures, the alveolar buds.

Calcium regulation of normal human mammary epithelial cell growth in culture

The concentration of Ca++ in culture media profoundly affected the growth and differentiation properties of normal human mammary epithelial cells in short-term culture. In media where Ca++ was above 0.06 mM, longevity was limited to an average of three to four cell divisions. The extended growth fraction (those cells able to divide more than once) was only approximately 50% and diminished to zero quickly with time. Stationary cells inhibited from dividing appeared differentiated in the formation of lipid vacuoles and accumulation of alpha-lactalbumin. Growth of stationary cultures could be reinstituted in about half the cells, either by disruption and transfer or by a reduction in Ca++ to less than 0.08 mM. The reduction of Ca++ to levels below 0.08 mM extended the longevity of normal cells to eight to nine divisions. The extended growth fraction was 100%. Under these conditions, cells did not differentiate. The effects of Ca++ on growth and differentiation were specific (Mg++ and Mn++ variations were without effect) and reversible and in many respects resembled Ca++ effects on epidermal cells. One major difference is that the dual pathways of growth and differentiation in mammary cells were controlled by glucocorticoid and insulin. Based on the kinetics of the reversible Ca++-induced coupling and uncoupling of proliferation and the program of differentiation, we proposed that Ca++ may be an essential trigger for cell divisions that commit a mammary cell to differentiate progressively in a permissive hormonal milieu.

Origin and extension of intraductal papillomas of the breast: a three-dimensional reconstruction study

Surgical specimens from fifteen patients with intraductal papilloma were reconstructed three-dimensionally from semi-serial sections to visualize the intraductal distribution of papillomas. Our results showed two basically different papillomas. In five patients, the papillomas were single and originated in the large ducts such as the segmental or subsegmental duct, but did not involve the terminal ductal-lobular units (TDLU); this type corresponded to the so-called solitary papilloma. In the remaining ten specimens, the papillomas were multifocal three-dimensionally; each had a root in the TDLU and spread into the large ducts, suggesting its purely peripheral origin. In view of this striking difference, and of possible canceration of ductal peripheries, a nomenclature of peripheral vs central papillomas is proposed instead of the conventional multiple vs solitary. Duct papillomatosis, invariably situated within the TDLU, was shown to be a continuation of peripheral papilloma and was regarded accordingly as a prepapillomatous condition.

The role of genotoxic carcinogens and of promoters in carcinogenesis and in human cancer causation

The majority of human cancers have multifactorial environmental causes stemming mainly from lifestyle factors such as use of tobacco products through cigarette smoking, snuff dipping, or chewing, and specific nutritional elements and dietary practices. The mechanisms of these lifestyle factors can be analyzed in terms of specific genotoxic carcinogens, and of epigenetic agents or promoting factors. Tobacco and tobacco smoke contain not only genotoxic carcinogens but also, with a more important ultimate effect, cocarcinogens and promoters. Alcohol acts as a cocarcinogen with tobacco, possibly by modifying the metabolism of carcinogens in select organs. Genotoxic carcinogens as nutritional factors may be found in pickled, salted, and smoked foods and may be responsible for gastric cancer. Vitamins C and E and other antioxidants are effective inhibitors. Other types of genotoxic carcinogens are mutagenic chemicals found in broiled and fried foods, and these may be involved in cancer of the colon, breast, and prostate. Promoting effects derive from a high level of dietary fat, which has been linked epidemiologically and through laboratory studies to a higher risk for these cancers. Possible mechanisms by which fat exerts its effects are an increased concentration of bile acids in the stool, as related to colon cancer, and which may be countered by a high cereal fiber diet, to increase stool bulk. In relation to breast or prostate cancer, fat may exert its effect on complex hormonal balances, and also on membrane composition. These promoting effects, whether associated with tobacco smoke or nutrition, are highly dose-dependent, and provided the insult is not too far advanced, reversible. Thus, lowering the dosage, or eliminating the effect as in smoking cessation should have an appreciable effect in reducing overt disease development, and do so fairly promptly. This may apply also to a reduction of second disease in cases where a first occurrence has been successfully treated by conventional means.

How culture conditions modulate the morphofunctional differentiation of the human estradiol-sensitive mammary cell line (MCF-7)

The MCF-7 cell line grown on plastic surfaces is widely accepted as a model for hormone sensitivity in molecular biology. However, in vitro results concerning estrogen sensitivity remain controversial. In search of culture conditions most closely simulating the in vivo microenvironment we cultured MCF-7 cells on diverse substrates and in suspension culture. The different factors of the contact environment: (A) influence of diffusive medium, (B) influence of cell to cell contacts, and (C) influence of cell to substrate contacts were considered. Using morphological criteria:phase contrast microscopy, scanning and transmission electron microscopy we observed MCF-7 morphofunctional differentiation under the different culture conditions. Plastic, corneal endothelial cell extracellular matrix, and attached collagen gels imposed a planar medium-aggregate interface. The impermeability of the free surface and the intense basal tension antagonized epithelial polarization. Only at post-confluence did domes and clusters appear above the monolayer. On floating collagen gels and in suspension culture the cells established intimate cell-cell contacts over large surfaces and reconstituted tissular architecture. Three-dimensional growth conditions which approach the in vivo contact environment of epithelial cells should be used instead of the traditional monolayer cultures for assessing hormonal and pharmacological responses of human breast carcinomas.

Interrupted pregnancy as an indicator of poor prognosis in T1, 2, N0, M0 primary breast cancer

We examined the records of women with primary breast cancer for a history of pregnancy and live births. The patients were all histopathologic T1, 2, N0, M0 white females, untreated post modified radical mastectomy. Patients with a history of interrupted pregnancies have a significantly shorter time to recurrence than those with normal pregnancy history. A trend toward a lower incidence of highly differentiated histological pattern is also observed in cancers from these patients.

Molecular and cellular basis of the mammary gland susceptibility to carcinogenesis

Mammary carcinomas induced by the administration of 7,12-dimethylbenz(a)anthracene (DMBA) to young virgin rats arise from undifferentiated terminal ductal structures called terminal end buds (TEBs). TEBs that normally differentiate into alveolar buds (ABs) and lobules under the influence of DMBA develop intraductal proliferations which progress to carcinoma. The high susceptibility of the young virgin rat TEBs to neoplastic transformation is due to its large proliferative compartment, with cells cycling every 10 hr, and to a higher (3)H-DMBA uptake. Progressive differentiation of TEBs into ABs and lobules or their regression to terminal ducts (TDs) is seen with aging. Complete differentiation of the gland is attained only through pregnancy and lactation. The greater differentiation of the gland is manifested as permanent structural changes, consisting in the disappearance of TEBs and in a diminution of the number of TDs due to their differentiation into ABs and lobules. This greater differentiation results in a diminished or total refractoriness of the gland to the carcinogen because ABs and lobules have a lower proliferative compartment and a longer cell cycle than TEBs and TDs. Cells of parous rats have both in vivo and in vitro a lower DMBA-DNA binding capacity, a lower DNA synthesis and a greater ability to repair DMBA damaged DNA than cells of young virgin rats. The more efficient DNA repair capacity of the parous rat mammary gland is demonstrated by the induction of unscheduled DNA synthesis and a removal of DMBA-DNA adducts.