The search for the causes of breast and colon cancer

The association of breast cancer and colorectal cancer in men. An analysis of surveillance, epidemiology, and end results program data

There is a known increased risk for the co-occurrence of both breast cancer and colorectal cancer in the same women, presumably as a result of either shared reproductive hormonal or environmental risk factors. Using data from the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute, the authors investigated whether there is a similar relationship between breast cancer, colorectal cancer, and prostate cancer in men. The observed-expected ratio was not significantly elevated for either colorectal cancer after breast cancer or for breast cancer after colorectal cancer in men. There was an increased incidence of prostate cancer after colorectal cancer, but this relationship was not present in the opposite direction and is believed to result from detection bias. There was an increased incidence of breast and colorectal cancer in women. These results suggest that the observed breast and colorectal cancer relationship in women may be a result of shared reproductive hormonal factors.

p53 mutations in human cancers

Mutations in the evolutionarily conserved codons of the p53 tumor suppressor gene are common in diverse types of human cancer. The p53 mutational spectrum differs among cancers of the colon, lung, esophagus, breast, liver, brain, reticuloendothelial tissues, and hemopoietic tissues. Analysis of these mutations can provide clues to the etiology of these diverse tumors and to the function of specific regions of p53. Transitions predominate in colon, brain, and lymphoid malignancies, whereas G:C to T:A transversions are the most frequent substitutions observed in cancers of the lung and liver. Mutations at A:T base pairs are seen more frequently in esophageal carcinomas than in other solid tumors. Most transitions in colorectal carcinomas, brain tumors, leukemias, and lymphomas are at CpG dinucleotide mutational hot spots. G to T transversions in lung, breast, and esophageal carcinomas are dispersed among numerous codons. In liver tumors in persons from geographic areas in which both aflatoxin B1 and hepatitis B virus are cancer risk factors, most mutations are at one nucleotide pair of codon 249. These differences may reflect the etiological contributions of both exogenous and endogenous factors to human carcinogenesis.

Adsorption of a hydrophobic mutagen to dietary fibre from the skin and flesh of potato tubers

One of the theories to explain the protective action of some dietary fibres against colon cancer is that certain mutagens and/or cancer promoters are adsorbed to these dietary fibres making the mutagens and/or cancer promoters less available to gut mucosal cells. The abilities of 2 contrasting cell wall preparations (dietary fibre preparations) from potato tubers to adsorb in vitro the hydrophobic mutagen, 1,8-dinitropyrene (DNP), were studied using an incubation mixture containing DNP in phosphate-buffered saline (PBS). Walls from potato skins strongly adsorbed DNP and, at the highest wall concentration tested, only a small porportion of the DNP remained in solution. In marked contrast to the skin walls, potato flesh walls adsorbed only a small proportion of the DNP. Unexpectedly, the flesh walls also caused a large increase in the proportion of DNP found in solution. When flesh walls were pre-extracted with PBS, the ability of the extracted walls to bind DNP increased. The material extracted from the flesh walls was able to maintain DNP in solution, when added to the incubation medium in the absence of cell walls. Pectic polysaccharides appear to be the soluble component responsible for maintaining the DNP in solution. Competition between soluble and insoluble fibre components may have major implications for the availability and distribution of hydrophobic mutagens in the alimentary tract.

Vegetable and fruit consumption and cancer risk

The relationship between cancer risk and frequency of consumption of green vegetables and fruit has been analyzed using data from an integrated series of case-control studies conducted in northern Italy between 1983 and 1990. The overall dataset included the following histologically confirmed cancers: oral cavity and pharynx, 119; oesophagus, 294; stomach, 564; colon, 673; rectum, 406; liver, 258; gall-bladder, 41; pancreas, 303; larynx, 149; breast, 2,860; endometrium, 567; ovary, 742; prostate, 107; bladder, 365; kidney, 147; thyroid, 120; Hodgkin's disease, 72; non-Hodgkin lymphomas, 173; myelomas, 117; and a total of 6,147 controls admitted to hospital for acute non-neoplastic conditions, unrelated to long-term dietary modifications. Multivariate relative risks (RR) for subsequent tertiles of vegetable and fruit consumption were derived after allowance for age, sex, area of residence, education and smoking. For vegetables, there was a consistent pattern of protection for all epithelial cancers, with RRs in the upper tertile ranging from 0.2 for oesophagus, liver and larynx to 0.7 for breast. All the trends in risk were in the same direction and significant for all carcinomas except gall-bladder. In contrast, no protection was afforded by high vegetable consumption against non-epithelial lymphoid neoplasms. With reference to fruit, strong inverse relationships were observed for cancers of the upper digestive and respiratory tract, with RRs in the upper tertile between 0.2 and 0.3 for oral cavity and pharynx, oesophagus and larynx relative to the lowest tertile. The lower the location of the tumour in the digestive tract, the weaker appeared to be the protection afforded. Significant inverse relationships were observed for liver, pancreas, prostate and urinary sites, but not for rectum, breast and female genital cancers or thyroid. No relationship emerged for lymphomas and myelomas. Even in the absence of a clear biological interpretation, the consistency and strength of the patterns observed indicate that, in this population, frequent green vegetable intake is associated with a substantial reduction of risk for several common epithelial cancers, and that fruit intake has a favourable effect, especially on upper digestive cancers and, probably, also on urinary tract neoplasms.

Colorectal cancer in northeast Italy: reproductive, menstrual and female hormone-related factors

The role of reproductive and menstrual factors and a few medical conditions linked to female hormones in the aetiology of colorectal cancer was investigated in a case-control study conducted in Pordenone province in northeastern Italy, on 89 women with colorectal cancer and 148 controls admitted to hospital for a wide spectrum of acute, non-digestive nor neoplastic disorders. After adjustment for age and social class, parous women, as compared to nulliparous ones, were significantly protected against colorectal cancer (odds ratio, OR = 0.4, [95% confidence interval, CI:0.2-0.8]) and the risk appeared to decrease with successive pregnancies up to five or more (0.2, [0.04-0.6]). Compared to women who had their first birth at age 24 or less, the OR for those who had it at 30 or older was 2.0, but the inverse trend in risk was not significant. However, among parous women only, age at first birth, but not parity, seemed to retain a certain influence. Late age at menopause seemed to decrease colorectal cancer risk (OR for menopause at age greater than or equal to 50 vs. less than 45 = 0.4, [0.2-1.0] chi 2(1) (trend) = 3.66). Conversely, age at last birth, number of abortions, years between marriage and first birth, age at menarche, pattern of menstrual cycle and occurrence of a few medical conditions potentially linked to female hormones were similarly reported by cases and controls. Due to the very limited number of oral contraceptive (OC) users (9 controls but only 1 case), and the lack of oestrogen replacement therapy users, the influence of exogenous female hormones on colorectal cancer could not be analysed meaningfully.

Reproductive factors and colorectal cancer

Descriptive and analytical epidemiology have suggested that cancer of the colorectum may have reproductive correlates similar to those of breast cancer (e.g., protection by parity and early age at first birth), but the evidence is still controversial. We therefore reviewed published data from 15 case-control investigations, two cohort studies, and one cancer registry-based study from seven different countries. With reference to parity, statistically significant protection for colorectal cancer was found in three case-control studies; in four other studies, significant inverse relationships of parity were observed with colon cancer, but not with rectal cancer. Among the remaining 12 studies, relative risks below unity for parous or multiparous women were observed in four. There was no appreciable trend in risk in four others; in two, there was nonsignificant increased risk with parity; and in one, a significant increased risk. Information on age at first birth was available from 12 studies. Three reported significant trends of increased risk with increasing age at first birth--one found a direct association of borderline significance; six indicated no evidence of association; and two reported an inverse trend in risk of borderline significance. Findings on age at menarche were inconsistent and mostly negative, although an inverse significant association was reported, especially regarding colon cancer, in one investigation. In all the six studies, which provided information on age at menopause, there was a hint of protection, although nonsignificant, for women who underwent natural menopause at an older age. Two studies reported a direct association of colorectal cancer with use of oral contraceptives, and another showed an inverse relationship with the use of menopausal estrogens.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption of a hydrophobic mutagen to five contrasting dietary fiber preparations

The ability of five plant cell wall (dietary fiber) preparations with contrasting compositions to adsorb in vitro the hydrophobic, environmental mutagen, 1,8-dinitropyrene (DNP), was investigated. Many of the fruits and vegetables in Western diets are from dicotyledonous (broad leaved) plants and the dietary fiber from these consists mainly of unlignified cell walls. A representative of this wall type, prepared from immature cabbage leaves, showed little ability to adsorb DNP. Two other cell-wall preparations, representing lignified walls of dicotyledons and unlignified walls of vegetative parts of grasses and cereals (monocotyledons belonging to the family Poaceae), adsorbed DNP much more effectively. However, two further preparations, representing suberized walls of cork cells and lignified walls of vegetative parts of grasses and cereals, were the most effective in adsorbing DNP. Extrapolation of these data to the in vivo situation would indicate that increased consumption of the vegetative parts of grasses or cereals and plant material containing cork cells, for example potato skins, could be effective in removing hydrophobic mutagens from potential contact with colonic mucosal cells.

A prospective study of body mass, height, and smoking on the risk of colorectal cancer in women

Female registered nurses in the United States who responded to a questionnaire in 1976 that inquired about height, weight, and smoking history were followed for the development of colon or rectal cancers through May of 1984. Among the 118,404 respondents free of cancer in 1976, 191 colon cancers and 49 rectal cancers were observed during 916,170 person-years of follow-up. After omitting cases diagnosed within two years of weight report, we found little overall relation of body mass (Quetelet's) index to colon cancer risk; however there was a suggestion of elevated risk for the heaviest category of body mass index (greater than or equal to 29 kg/m2, relative risk (RR) = 1.5; 95 percent confidence interval = 0.8 - 2.7) relative to the lowest category (less than 21 kg/m2). Self-reported body mass index from adolescence had a slightly more pronounced, although not significant, association with risk of colon cancer. Increasing height was significantly associated with colon cancer (RR = 1.6, 95 percent confidence interval = 1.1 - 2.5 for the tallest category [greater than or equal to 168 cm] versus the shortest (less than 160 cm], trend, P = 0.04). Measures of current or past smoking failed to demonstrate any consistent relationship with colon cancer.

Dietary modulation of experimental neoplastic development: role of fat and fiber content and calorie intake

Cancer is still one of the major causes of death in the industrialized countries but locally prevailing lifestyles may dictate the kinds of cancer seen among populations of different geographical areas. Dietary habits and, in particular, the nature and/or the amount of fat, calorie and/or vegetable fiber which are consumed in these countries are among the most frequently quoted etiological factors which may account for this situation. Epidemiological and experimental evidence has accumulated which, even though it can be used to support these conclusions, is still a matter of considerable debate. Modulation of neoplastic development is a concept which has been elaborated to overcome the fact that many experimental observations are not really taken into consideration by the classical 2-step theory of carcinogenesis. It is defined as the effect of any treatment which given before, during or after the initiation of a full carcinogenic process modifies the pattern of neoplastic development as evaluated by the kinetics of appearance, the incidence and/or the yield of histologically characterized malignant tumors. It is said to be positive or negative depending on whether it accelerates or slows down the process and increases or decreases the yield of malignant tumors respectively. From a review of the available experimental data, it is concluded that fat per se has, most probably, no modulating effect but that unbalanced diets rich in lipids could act as a positive modulator of chemically induced carcinogenesis by virtue of their capacity to cause a break in metabolic and proliferative homeostasis; that vegetable fibers as well as restriction in calorie intake could act as negative modulators of the same process because they could restore or help restore this homeostasis. It is thus proposed that to maintain dietary balance either by increasing fiber and/or by reducing total calorie intake is the most effective way to negatively modulate chemically induced carcinogenesis in experimental animals. To make the same recommendation to humans could most probably help preventing major cancers like breast and colon cancers.

Is the incidence of colorectal cancer related to reproduction? A prospective study of 63,000 women

Relationships between reproductive factors and risk of colorectal cancer were examined in a population-based prospective study in Norway. Available for analysis were 831 cases (581 colon cancer, 250 rectal cancer) diagnosed in a cohort of 63,090 women, surveyed in 1956-1959 and followed through 1980. Overall, the analyses showed no strong effects of reproductive factors. In particular, high parity was not associated with reduced risk, and late age at first or last birth was not associated with an increased overall risk. However, in age-specific analyses of colon cancer, adverse effects of late age at first birth and late age at last birth were observed in women with cancer diagnosed before the age of 60. A non-significant overall excess risk in parous compared to nulliparous women was strongest for women with a cancer diagnosis before the age of 50 years. Having had many abortions was associated with increased risk for all sub-sites. Neither age at menarche nor age at menopause were related to risk of colorectal cancer. The results suggest that reproductive factors, which are of importance in the etiology of cancer of the breast and genital organs in women, are not similarly related to risk of colorectal cancer.

Cancer incidence among parents of patients with colorectal cancer

To investigate the genetic factor in the development of colorectal cancer, a cohort study was undertaken of parents of patients with this disease. All 1,524 patients, who were diagnosed with colorectal cancer in Denmark in 1982-84 and were below the age of 60 years, were selected from the National Cancer Register. The parents of these patients were identified from the public population registers. The index persons had a total of 1,478 eligible mothers, of whom 96% were successfully traced, and a total of 1,414 eligible fathers, of whom 96% were traced. These parents were sought in the Cancer Register for cancer cases diagnosed in the period January 1, 1943 to December 31, 1986. The incidence rates for the Danish population were used to estimate the expected numbers of colorectal cancer cases among the parents. Both the mothers and the fathers exhibited an increased risk of colorectal cancer. The standardized incidence ratios were 1.62 (95% CI 1.31-2.01) and 1.87 (95% CI 1.54-2.27), respectively. In a previous study we found that spouses of patients with colorectal cancer in Denmark did not have an increased risk of this disease. The increased risk found in the present study among the parents of patients therefore indicates that a possible genetic factor is present in the aetiology of colorectal cancer, and that it is of importance in the general population.

Breast size, handedness and breast cancer risk

Bra cup size and handedness were studied as possible risk factors for breast cancer. Data for 3918 cases and 11,712 controls from 7 centres were used to examine the association of handedness with laterality of breast cancer; data for 2325 cases and 7008 controls from 4 centres were used to assess the relation of bra cup size to breast cancer risk. There was a suggestive (P about 0.10) association of handedness with breast cancer laterality: odds ratio of a left-handed (or ambidextrous) woman having a left-sided cancer 1.22 (95% CI 0.96-1.56). Handedness may affect the lateral occurrence of breast cancer, although this tumour is in general more common in the left breast, possibly because this breast is usually slightly larger. Premenopausal women who do not wear bras had half the risk of breast cancer compared with bra users (P about 0.09), possibly because they are thinner and likely to have smaller breasts. Among bra users, larger cup size was associated with an increased risk of breast cancer (P about 0.026), although the association was found only among postmenopausal women and was accounted for, in part, by obesity. These data suggest that bra cup size (and conceivably mammary gland size) may be a risk factor for breast cancer.

Oestrogen and progesterone receptors in primary breast cancer: a population study

The results of a single centre study on cytoplasmic oestrogen (ER) and progesterone (PR) receptors and their combinations in primary breast cancer of 1957 patients from various parts of Croatia are presented. The frequency of ER+ tumours and tumour mean ER concentration were higher in patients over 50 years of age, while PR frequency and concentration were similar in patients over and under 50. The ER concentration was positively correlated with the age of patients, but the age-related increase in ER concentration appeared between 50 and 70 years of age. The pattern of receptor coexistence was age related. The frequency of ER+PR+ and ER+PR- increased and that of ER-PR+ and ER-PR- tumours decreased with the age of patients. The concentrations of ER and PR were higher in ER+PR+ than in ER+PR- or ER-PR+ tumours, respectively. When the patients were divided into groups under and over 50 years of age these differences appeared only in the latter group, while in the former the concentrations of ER were similar in ER+PR+ and in ER+PR- tumours, and the concentration of PR was higher in ER+PR+ than in ER-PR+ tumours. These data suggest a biological difference between breast cancers with various receptor combinations, as well as a difference in pathogenesis of the receptor negative and positive breast cancer.

Bile salt/acid induction of DNA damage in bacterial and mammalian cells: implications for colon cancer

Two bile salts, sodium chenodeoxycholate and sodium deoxycholate, induced a DNA repair response in the bacterium Escherichia coli. Similarly, a bile acid and a bile salt, chenodeoxycholic acid and sodium deoxycholate, induced DNA repair (indicated by unscheduled DNA synthesis) in human foreskin fibroblasts. Also, DNA repair-deficient Chinese hamster ovary (CHO) cells were found to be more sensitive than normal cells to killing by bile salts. In particular, mutant UV4 CHO cells, defective in DNA excision repair and DNA cross-link removal, were more sensitive to sodium chenodeoxycholate, and mutant EM9 CHO cells, defective in strand-break rejoining, were more sensitive to sodium deoxycholate than wild-type cells. These results indicate that bile salts/acid damage DNA of both bacterial and mammalian cells in vivo. Previous epidemiological studies have shown that colon cancer incidence correlates with fecal bile acid levels. The findings reported here support the hypothesis that bile salts/acids have an etiologic role in colon cancer by causing DNA damage.

Starchy foods and colon proliferation in mice

The effect of starch contained in different foods on colonic proliferation was studied in C57BL/6N mice after four weeks of feeding with 20% fat diets containing cornstarch, white bread, pasta, and rice; an equicaloric amount of sucrose was used in a control diet. Cell proliferation was evaluated in different subsites of the colon (rectal end, mid colon and cecal end) by colchicine arrest and [3H]thymidine incorporation. The following parameters were analyzed: mitotic index (MI), labeling index (LI), and the distribution of labeled cells along the crypt. Different results were obtained in the different subsites. At the rectal end of the colon, all diets containing starch lowered cell proliferation compared with the sucrose diet. The values for MI in the different diets were 2.56 +/- 0.22, 1.73 +/- 0.30, 1.37 +/- 0.19, 1.61 +/- 0.29, and 1.29 +/- 0.31 for control, cornstarch, white bread, pasta, and rice, respectively. Values are means +/- SE (n = 10). The values for LI showed a similar pattern. In the mid colon, the MI was significantly lowered only by the diet containing rice, whereas the DNA synthetic activity (LI) was lowered by cornstarch, pasta, and rice. Toward the cecal end, we observed a significant reduction in MI with diets containing pasta and rice and in the LI with diets containing pasta. The distribution of the LI along the crypt in the different subsites was not significantly affected by experimental dietary variations. The results suggest that starch from different dietary sources might reduce colon proliferation in the mouse.

Physical activity, dietary habits and adenomatous polyps of the sigmoid colon: a study of self-defense officials in Japan

Physical activity and dietary habits were compared between 80 men with adenomatous polyps of the sigmoid colon and 1148 men with normal colonoscopy among male retiring self-defense officials. Physical activity as expressed in terms of time spent doing strenuous activities during leisure time was inversely related to the risk of adenomatous polyps. Controlling for rank, smoking, alcohol and body mass index (BMI), odds ratios for the categories of 0, 1-59, 60-119 and greater than or equal to 120 minutes per week were 1.0, 0.88, 0.70 and 0.44, respectively (trend p = 0.015). Among a limited range of foods and beverages, the consumption of rice, green tea and instant coffee tended to be associated with a decreased risk of adenomatous polyps. Although the associations observed with dietary habits still need to be substantiated, the findings on physical activity lend further evidence to the hypothesis that physical activity may be protective in the development of colon cancer.

A novel metalloproteinase gene specifically expressed in stromal cells of breast carcinomas

A gene has been identified that is expressed specifically in stromal cells surrounding invasive breast carcinomas. On the basis of its sequence, the product of this gene, named stromelysin-3, is a new member of the family of metalloproteinase enzymes which degrade the extracellular matrix. The suggestion is that stromelysin-3 is one of the stroma-derived factors that have long been postulated to play an important part in progression of epithelial malignancies.

Relation of meat, fat, and fiber intake to the risk of colon cancer in a prospective study among women

BACKGROUND

The rates of colon cancer in various countries are strongly correlated with the per capita consumption of red meat and animal fat and, to a lesser degree, inversely associated with the consumption of fiber.

METHODS

We conducted a prospective study among 88,751 women 34 to 59 years old and without a history of cancer, inflammatory bowel disease, or familial polyposis who completed a dietary questionnaire in 1980. By 1986, during 512,488 person-years of follow-up, 150 incident cases of colon cancer had been documented.

RESULTS

After adjustment for total energy intake, animal fat was positively associated with the risk of colon cancer (P for trend = 0.01); the relative risk for the highest as compared with the lowest quintile was 1.89 (95 percent confidence interval, 1.13 to 3.15). No association was found for vegetable fat. The relative risk of colon cancer in women who ate beef, pork, or lamb as a main dish every day was 2.49 (95 percent confidence interval, 1.24 to 5.03), as compared with those reporting consumption less than once a month. Processed meats and liver were also significantly associated with increased risk, whereas fish and chicken without skin were related to decreased risk. The ratio of the intake of red meat to the intake of chicken and fish was particularly strongly associated with an increased incidence of colon cancer (P for trend = 0.0005); the relative risk for women in the highest quintile of this ratio as compared with those in the lowest quintile was 2.49 (95 percent confidence interval, 1.50 to 4.13). A low intake of fiber from fruits appeared to contribute to the risk of colon cancer, but this relation was not statistically independent of meat intake.

CONCLUSIONS

These prospective data provide evidence for the hypothesis that a high intake of animal fat increases the risk of colon cancer, and they support existing recommendations to substitute fish and chicken for meats high in fat.

Diet, body mass and colorectal cancer: a case-referent study in Stockholm

A population-based case-referent study on diet (total energy, protein, fat, dietary fiber), body mass and colorectal cancer was performed in Stockholm in 1986-1988. The study included 1,081 subjects. The relative risks (RR, with a 95% confidence interval, highest versus lowest quintile) for colon cancer were as follows: total energy (1.7, 1.0-3.0), protein (2.4, 1.5-4.0), total fat (2.2, 1.3-3.6), dietary fiber for men (0.5, 0.2-1.1), dietary fiber for women (1.2, 0.7-2.3) and body mass (2.0, 1.3-3.1). The relative risks for rectal cancer were: total energy (2.4, 1.2-4.7), protein (3.6, 2.0-6.4), total fat (2.5, 1.4-4.6), dietary fiber (0.5, 0.3-0.9), body mass for men (1.7, 0.7-4.0), and body mass for women (1.0, 0.5-1.9). Adjustment for physical activity, body mass (in the diet analysis), the above-mentioned dietary factors (in the body mass analysis), and browned meat surface had little or no influence on the results.

Cancer genes: current status, future prospects, and applications in radiotherapy/oncology

There is a sense of excitement in contemporary cancer research, generated largely by the discovery, and subsequent characterization, of oncogenes. These genes are part of the normal complement of cells, and become altered in their structure or expression, during the development of the neoplastic phenotype. In this review, I highlight some of the important advances in the field, starting with the relationships between viral oncogenes and their cellular homologs. I illustrate some of the molecular mechanisms whereby a harmless, or quiescent, cellular gene can be converted ("activated") by radiation or by other carcinogens to a full-blown oncogene involved in carcinogenesis. Next, I discuss two areas where oncogene research has specific relevance for professionals working with radiation, namely the question of radiation-induced cancer, and the issue of the radiocurability of tumors. I also assess the important role of tumor-suppressor genes in oncogenesis. I then describe a genetic model, to illustrate the current status of our understanding of carcinogenesis. Finally, I discuss potential applications of specific interest to oncologists: topics such as prognostic indicators, novel therapeutic strategies, and gene-replacement techniques, are critically reviewed.

Effects of bile salts on the adsorption of a hydrophobic mutagen to dietary fiber

The effect of the bile salts, sodium cholate, deoxycholate, glycocholate and taurocholate, on the solubility in aqueous solution of the hydrophobic, environmental mutagen, 1,8-dinitropyrene (DNP), was examined. In the absence of bile salts, the DNP appeared to precipitate out of solution, whereas bile salts at a concentration of greater than or equal to 4 mM maintained the DNP in solution. In the presence of the model dietary fiber, alpha-cellulose, the DNP absorbed to this preferentially. Bile salts reduced this adsorption at low alpha-cellulose levels, but had little effect at high alpha-cellulose levels. The implication of these results is that bile salts have solubilising properties that could affect the distribution of hydrophobic molecules, including mutagens, in the digestive tract.

Nutrition and breast cancer

International comparisons have provided striking correlations between fat consumption and risk of breast cancer, but these comparisons do not often consider variations in life style. Case-control studies carried out in several countries showed no real association between fat intake and breast cancer. There is some evidence that vitamin A or carotenoid intake may exert a protective effect. Alcohol intake, on the other hand, seems to be positively associated with breast cancer risk. Elevated body weight, body mass, stature, and frame size have been found to be associated as risk factors for breast cancer in women. Animal studies found that caloric restriction inhibits growth of spontaneous and induced mammary tumors, an observation that held up even when the calorie-restricted animals ingest more fat than the ad-libitum-fed controls. College women who exercise have a lower incidence of breast cancer than their more sedentary classmates. Exercise is another means of reducing caloric availability.

What can a woman do about her risk of dying of breast cancer?

Every day, American women are told that one in ten will develop breast cancer, and some groups perceive their risk to be so high as to justify immediate bilateral mastectomy. Many associations with breast cancer have been identified, including a history of benign breast diseases, in situ carcinoma, a family history of breast cancer, prolonged menstruation as a result of early menarche or delayed menopause, few or late pregnancies, excessive alcohol intake, obesity, and possibly the use of estrogens as oral contraceptives or postmenopausal replacement therapy. In spite of these associations, our understanding of either the cause(s) of breast cancer or the sequence of events leading to a diagnosis of breast cancer is still inadequate to make global public health recommendations regarding life style--or even to initiate well-designed studies. The epidemiologic evidence strongly suggests, however, that events relatively early in a woman's life are more important than later events, even though most of the risk of developing breast cancer will be expressed after the age of 75. Possibly one of the greatest contributions we can make to our patients' welfare is to share the knowledge that the risk of dying of breast cancer is considerably smaller than the risk of developing breast cancer; that the risk of early death from breast cancer rarely exceeds 10% in even the highest risk groups; and that the life styles most likely to reduce the risk of cardiovascular disease and other scourges of womankind are also those most likely to reduce the risk of developing breast cancer.

The importance of N-6 and N-3 fatty acids in carcinogenesis

Cross-cultural comparisons show that total fat intake is related to breast and colon cancer mortality. Total fat consists of different fatty acid families. Therefore different fatty acids should be studied in relation to breast and colon carcinogenesis. Animal experiments suggest that N-6 polyunsaturated fatty acids may have a tumor promoting effect and that N-3 polyunsaturated fatty acids may exert an inhibitory effect on chemically-induced mammary and colon tumorigenesis. Data from epidemiologic studies in this area are scarce. Comparisons between Japan and Iceland and between Eskimos and Danes suggest that a low-fat diet in combination with a N-3/N-6 polyunsaturated fatty acid ratio of about 0.5 seems to be associated with low mortality rates from breast and colon cancer. Much more research is needed to determine the optimal intake of total fat, N-6 and N-3 polyunsaturated fatty acids in relation to breast and colon cancer prevention.

A model system for studying the adsorption of a hydrophobic mutagen to dietary fibre

The adsorption of 1,8-dinitropyrene (DNP) to alpha-cellulose has been studied as a model system for examining the adsorption of a hydrophobic mutagen to dietary fiber. Most of the DNP rapidly disappeared from an aqueous solution and partitioned between the glass wall of the test tube and the alpha-cellulose. Factors affecting DNP distribution included (i) the time of incubation, (ii) the final concentration of the solvent, dimethyl sulphoxide, in which the DNP has been dissolved, and (iii) the relative concentrations of DNP and alpha-cellulose. We suggest that this model system could be applied to other mutagens, and that alpha-cellulose would provide a useful standard fiber to permit inter-laboratory comparisons.

Hypothesis: does breast cancer originate in utero?

Factors that increase the risk of cancer during adult life may also increase the risk of cancer when they act in utero (eg, ionising radiation and diethylstilboestrol in human beings and chemicals in animals). The existing empirical data seem to be compatible with the hypothesis that increased concentrations of oestrogens in pregnancy increase the probability of future occurrence of breast cancer in daughters.

Familial cancer syndromes and clusters

Familial aggregation has been reported for virtually every form of cancer in humans. In general, close relatives of a cancer patient appear to have a twofold to threefold increase in risk for that tumor. Among cancer families, however, the level of excess risk is heterogeneous and ranges up to 1000-fold. Familial clusters of cancer are often due to inherited susceptibility, but environmental influences and chance association also must be considered. The effect of chance is large, due to the 50% lifetime risk of developing cancer that is present in the general U.S. population. Thus, a family history of cancer is the rule rather than the exception, and special studies are needed to distinguish predisposition from chance. An inherited susceptibility to cancer often becomes apparent through the occurrence of the same neoplasm among multiple blood relatives. These neoplasms tend to occur at earlier ages than usual, to appear bilaterally in paired organs, and to develop in multiple primary foci within the predisposed organ. Hereditary cancers can also develop as multiple primary tumors in organs that share the same embryological origins, as in the multiple endocrine neoplasia (MEN) syndromes. In addition, neoplasia occurs as a feature of diverse inherited diseases, such as neurofibromatosis types 1 and 2, which predispose to tumors of the peripheral nerves and brain. Recent advances in molecular biology have greatly enhanced the importance of studying cancer families. Newly developed molecular probes have been applied to map the loci of several human cancer genes. The studies have also revealed a new class of human oncogenes, the tumor suppressor genes. These genes normally function by suppressing the tumor phenotype. When inactivated or deleted in germinal cells, they can be transmitted to subsequent generations and predispose to cancer among carriers in the family. At the molecular level, these carriers have inherited a structural abnormality in one allele of a recessive oncogene, and loss of the second allele at the locus results in tumor development. The first tumor suppressor that has been isolated is the retinoblastoma gene on chromosome 13q14. Studies indicate that this gene is involved in the development of many more human cancers than had been appreciated previously on the basis of clinical observations. Presently, the identification of cancer families can be applied to genetic counseling, the in-utero diagnosis of carriers, and early disease detection. In familial cancers that are triggered by environmental carcinogens, patient education regarding the avoidance of harmful exposures can help prevent or delay the onset of neoplasia.

Hypotheses for the etiology of colorectal cancer--an overview

Colorectal cancer is the second most common cancer in the United States. Various dietary, colonic, and fecal components have been implicated as causative factors. Although numerous studies have been conducted to test them, so far no one factor has stood out as the most likely cause of colorectal cancer. This review presents the evidence for and against the major factors and concludes that bile acids are the most strongly implicated factors in the etiology of colorectal cancer.

Oncogenes and tumor growth factors in breast cancer. A minireview

Five oncogenes have been implied as having a role in human breast tumorigenesis: int-2, c-erbB-2 (HER-2), c-myc, c-Ha-ras and the recessive Rb-1. As far as the function and biochemistry of these oncogenes have been studied, they act at different levels and have totally different functions in the cells. They are normally cellular genes, likely to have important functions in normal cell growth or differentiation. In the tumors their regulation or function is altered, due to a wide class of mutations. The oncogenes may cooperate to result in the malignant cell phenotype. However, different oncogenes are mutated in different tumors, so that the tumors show a variable pattern at the molecular level, underlining the individuality of these tumors already described as differences in histopathology, hormone receptor expression and clinical course. The main importance of the oncogene studies is still to reveal basic pathogenetic mechanisms. When appropriate it is important to test diagnostic or prognostic significance of the oncogene mutations.