Insulin and related factors in premenopausal breast cancer risk

Review of anthropometric factors and breast cancer risk

Epidemiological evidence implicating anthropometric risk factors in breast cancer aetiology is accumulating. For premenopausal women, breast cancer risk increases with increasing height, but decreases with higher weight or body mass index, and no association with increased central adiposity exists. For postmenopausal women, an increased risk of breast cancer is found with increasing levels of all the anthropometric variables including height, weight, body mass index, waist-hip ratio, waist circumference and weight gain. Weight loss appears to decrease risk, particularly if it occurs later in life. Breast size may be a risk factor for breast cancer, however, the current evidence is inconclusive. Several hypothesized biologic mechanisms exist to explain how anthropometric factors influence breast cancer risk. Obesity may increase levels of circulating endogenous sex hormones, insulin and insulin-like growth factors that all, in turn, increase breast cancer risk. Genetic predisposition to obesity and to specific body fat distributions are also implicated. With obesity, there are increased levels of fat tissue that can store toxins and can serve as a continuous source of carcinogens. Recommendations for future research on anthropometric factors and breast cancer are provided. Sufficient evidence exists to support strategies to avoid weight gain throughout life as a means of reducing postmenopausal breast cancer risk.

The relation of type 2 diabetes and cancer

Increasing evidence indicates that individuals with type 2 diabetes (diabetes) are at elevated risk for several common human malignancies, including cancers of the colon, breast, endometrium, pancreas, and liver. In particular, the consistent positive results reported by prospective investigations make it unlikely that methodologic issues, occult tumors, or chance results could explain the findings. Since diabetes and impaired fasting glucose together affect >25% of Americans above age 50, even a moderate etiologic association (e.g., relative risk = 1.5) would explain >10% of involved malignancies. Laboratory studies have suggested biologically plausible mechanisms. Insulin, for example, is typically at high levels during the development and early stages of diabetes. Activation of the insulin receptor by its ligand, or cross-activation of the insulin-like growth factor-I receptor, has been shown to be mitogenic and promote tumorigenesis in various model systems. A "unifying concept," in fact, holds that hyperinsulinemia may underlie the cancer associations of several additional risk factors, including high waist circumference, visceral fat, waist-to-hip ratio, body mass index, sedentary lifestyle, and energy intake. In this review, we assess current evidence regarding the relation of type 2 diabetes with cancer, and evaluate the findings in terms of well-accepted criteria for establishing causality.

Hyperinsulinemia: the missing link among oxidative stress and age-related diseases?

Mounting evidence supports Harman's hypothesis that aging is caused by free radicals and oxidative stress. Although it is known that oxidant species are produced during metabolic reactions, it is largely unknown which factor(s), of physiological or pathophysiological significance, modulate their production in vivo. In this hypothesis paper, it is postulated that hyperinsulinemia may have such function and therefore promote aging, independently of elevations of glycemia. Hyperinsulinemia is secondary to impaired insulin stimulated glucose metabolism at the level of skeletal muscle (insulin resistance) and is seen in about one third of glucose tolerant humans following dietary carbohydrate intake. If other insulin-stimulated (or inhibited) pathways retain normal sensitivity to the hormone, hyperinsulinemia could, by its effects on antioxidative enzymes and on free radical generators, enhance oxidative stress. Other proaging effects of insulin involve the inhibition of proteasome and the stimulation of polyunsaturated fatty acid (PUFA) synthesis and of nitric oxide (NO). The hypothesis that hyperinsulinemia accelerates aging also offers a metabolic explanation for the life-prolonging effect of calorie restriction and of mutations decreasing the overall activity of insulin-like receptors in the nematode Caenorhabditis elegans.

Serum insulin-like growth factor-I and breast cancer

Insulin-like growth factor I (IGF-I) is a systemic hormone with potent mitogenic and anti-apoptotic properties, which could influence the proliferative behavior of normal breast cells. Limited epidemiological observations suggest that the hormone may play a role in the etiology of breast cancer, especially at pre-menopausal ages. In a prospective case-control study nested within a cohort of New York City women, IGF-I, IGF-binding protein 3 (IGFBP-3) and C peptide were measured in frozen serum samples from 172 pre-menopausal and 115 post-menopausal subjects who were subsequently diagnosed with breast cancer. Subjects were eligible if diagnosed 6 months or more after recruitment into the study (7 to 120 months). Cohort members who matched the cases on age, menopausal status, date of blood sampling and day of menstrual cycle at blood collection served as controls. Post-menopausal breast cancer was not associated with serum IGF-I, IGFBP-3 or C-peptide levels. However, the risk of breast cancer increased with increasing serum concentrations of IGF-I in pre-menopausal women. The odds ratio (OR) for the highest quartile of IGF-I (>256 ng/ml) compared to the lowest (<168 ng/ml) was 1.60 [95% confidence interval (CI) 0.91-2. 81]. The OR decreased to 1.49 (95% CI 0.80-2.79) after adjustment for IGFBP-3. In analyses restricted to subjects who were pre-menopausal at the time of blood sampling and whose cancer was diagnosed before age 50, the top vs. bottom quartile OR increased appreciably to 2.30 (95% CI 1.07-4.94). Adjustment for IGFBP-3 reduced the OR to 1.90 (95% CI 0.82-4.42). There was no association between pre-menopausal breast cancer and IGFBP-3, IGF-I:IGFBP-3 ratio or non-fasting levels of C peptide. Elevated circulating levels of IGF-I may be an indicator of increased risk of breast cancer occurring before age 50.

Down-regulation of insulin-like growth factor-I receptor and insulin receptor substrate-1 expression in advanced human breast cancer

The ligands, receptors and related signaling proteins of the insulin-like growth factor family are involved in the regulation of breast-cancer cell growth. We investigated the expression pattern of insulin-like growth factor-I receptor (IGF-IR), insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), a core downstream signaling protein, in 69 primary breast-cancer specimens of different grades and in 21 control tissues by immunohistochemistry. In addition, cell proliferation (percentage of Ki67(+) nuclei) and estrogen receptor (ER) expression were determined. IGF-IR, IRS-1 and IR were expressed mainly in epithelial cells. IRS-1 and IGF-IR were expressed at high levels in control tissues and in well and moderately differentiated carcinomas but at low levels in poorly differentiated breast cancers. IR expression did not show a significant correlation with the differentiation grade of the tissues investigated. Statistical analysis (ROC analysis for tumor grade) demonstrated that down-regulation of IGF-IR and IRS-1 correlated better with tumor progression than reduction of ER expression or increase in cell proliferation, IGF-IR showing the best correlation, followed by IRS-1 and, less significant, ER and Ki67. Our findings clearly show that progression of breast cancer is accompanied by a reduction of IGF-IR/IRS-1 expression and that IGF-IR/IRS-1 expression inversely correlates with high proliferation rate in dedifferentiated breast cancers. The strong correlation of IGF-IR and IRS-1 down-regulation with tumor progression suggests the use of IGF-IR and IRS-1 as a novel set of marker proteins for tumor grading.

Relations of insulin resistance and serum concentrations of estradiol and sex hormone-binding globulin to potential breast cancer risk factors

There is a hypothesis that hyperinsulinemia or insulin resistance may be a mediator for breast cancer risk factors. On the other hand, some, but not all, of the well-known risk factors of breast cancer have been associated with serum estrogen concentrations. We assessed the relationships of potential breast cancer risk factors to indicators of insulin resistance, fasting plasma insulin concentration and homeostasis model assessment insulin resistance (HOMA-R), in 88 postmenopausal Japanese women. We also examined whether insulin resistance would explain the association of breast cancer risk factors with serum estradiol and sex hormone-binding globulin (SHBG). Information on potential breast cancer risk factors, such as demographic characteristics, smoking and drinking habits, diet, exercise, menstrual and reproductive factors, was obtained by self-administered health questionnaire including a validated semiquantitative food frequency questionnaire. Body mass index (BMI) was significantly correlated with the ratio of estradiol to SHBG (Spearman r = 0.30, P = 0.0004), fasting plasma insulin (r = 0.45) and HOMA-R (r = 0.43, P = 0.0001) after controlling for age. The correlations were still significant between BMI and estradiol / SHBG ratio (r = 0.21, P = 0.047) after controlling for fasting plasma insulin and between BMI and fasting plasma insulin (r = 0.40, P = 0. 0001) as well as HOMA-R (r = 0.38, P = 0.0003) after controlling for estradiol / SHBG ratio. There is a possibility that effect of BMI on breast cancer risk is mediated by both insulin resistance and estrogen metabolism.

Management of familial breast cancer risk

Women who are members of breast cancer families are at increased risk for breast cancer. The cloning of BRCA1 and BRCA2 has made it possible to identify mutation carriers within some of these families. Management of breast cancer risk in these families, which presents enormous challenges to patients and clinicians, is addressed. Management should begin with a full evaluation of the patient, including construction of a three-generation pedigree, ascertainment of non-genetic factors that may impact on risk, information on previous and current breast health, practice of and attitudes toward screening, and the psychosocial impact of family history on the individual. Patient priorities in risk management should be explicitly reviewed; these may include survival, cancer prevention, breast preservation, optimization of quality of life or minimization of disruption of day-to-day activities. Approaches to risk management involve screening (usually considered the mainstay), anti-estrogens, prophylactic surgery and/or lifestyle modifications. Specific gene therapy may become available in the future. Management decisions should be individualized to reflect risk levels and patient priorities and goals, within bounds that are medically and scientifically reasonable. An explicit examination of different time-frames (1, 5, 10 years) is recommended given the rapid evolution of knowledge in this area.

Adiposity as a risk determinant for postmenopausal breast cancer

BACKGROUND

Cross-cultural studies have long suggested that the high incidence of breast cancer in developed Western countries may be linked to the high prevalence of obesity and to high total energy intake. Recent studies show that hyperinsulinemia, increased concentration of insulin-like growth factor 1 and greater abdominal fat accumulation are markers of high risk for breast cancer. Increased serum concentrations of free estradiol and free testosterone are similar risk markers and are frequent concomitants of hyperinsulinemia.

MECHANISMS

The mechanism by which such metabolic-endocrine abnormality may promote mammary carcinogenesis is uncertain, but its effect is likely to predominate in the years approaching the menopause when obesity is common among Western women. In obese subjects, enlargement of adipose deposits is known to produce an excess of free fatty acids and tumor necrosis factor alpha, both of which may be involved in the pathogenesis of insulin resistance. In middle-aged women, the concomitants of hyperinsulinemia may activate invasive and proliferative activity in preneoplastic mammary lesions such as in situ duct carcinoma of the comedo type. This will enhance the risk of progression to invasive breast cancer, which is likely to manifest clinically mainly after the menopause.

CONCLUSION

Weight reduction combined with a program of regular physical exercise has been shown to reduce both estrogen and insulin concentrations in obese women and such a regimen might be tested in clinical trials for an effect on breast cancer risk in obese women. Intervention is best begun around the age of 45 y, this being the age when in situ duct carcinoma would normally begin to show evidence of spontaneous involution in women without clinical evidence of invasive breast cancer. International Journal of Obesity (2000) 24, 527-533

Biological mechanisms in breast cancer invasiveness: relevance to preventive interventions

Migration studies suggest that the high incidence of postmenopausal breast cancer in Western women is related mainly to epigenetic factors. Progression from ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) also appears to involve environmental rather than genetic factors, and a role has been postulated for metabolic-endocrine changes related to the Western lifestyle. Protein kinase C (PKC) is important in cell signal transduction, and laboratory studies show that PKC stimulates the activities of urokinase plasminogen activator, matrix metalloproteinases and cell adhesion molecules, all of which are known to increase invasiveness in human mammary cancer cell lines. In rodents, the activity of PKC in tissue cells is enhanced by insulin, and PKC isoenzymes have been shown to stimulate the development of hyperinsulinaemic insulin resistance in rodents. Clinically, hyperinsulinaemia and the concomitant increase in circulating levels of free oestradiol and bioactive insulin-like growth factor 1 (IGF1) are each confirmed markers of high risk for breast cancer in women. Lesions of DCIS show evidence of regression with mammary involution, but it is postulated that this may be opposed by the concomitants of hyperinsulinaemic insulin resistance. The prevalence of the latter is increasing in Western populations, and a combination of high IGF1 and low IGF-binding protein 3 concentrations has been associated with the presence of DCIS lesions in premenopausal women. Measures that enhance insulin sensitivity in such women may reduce the risk of progression in DCIS lesions, and a clinical trial is proposed to test the hypothesis.

Predisposition to colonic dysplasia is unaffected by continuous administration of insulin-like growth factor-I for twenty weeks in a rat model of chronic inflammatory bowel disease

BACKGROUND

Insulin-like growth factor-I (IGF-I) is currently under evaluation for the treatment of a variety of chronic disease conditions. We investigated the safety of long-term IGF-I administration in a rat model of inflammatory bowel disease which predisposes to the development of dysplasia.

METHODS

Chronic consumption of dextran sulphate sodium (DSS) by rats manifests a colitis with dysplastic features. Rats consumed 2% DSS for 4 weeks when pumps were implanted to deliver either vehicle or IGF-I for 15 or 20 weeks while rats continued to consume DSS. Features of colitis and dysplasia were assessed at kill.

RESULTS

Compared to vehicle, 20 weeks IGF-I significantly increased body weight by 19% and total gut weight by 43%. Colonic crypt depth, proliferative compartment, labelling index, dysplasia, neoplasia and other indices of colitis were not significantly affected.

CONCLUSIONS

Twenty weeks administration of IGF-I to rats induced growth of the intestine but did not affect the severity of experimentally-induced colitis or the incidence or progression of colonic dysplasia.

Alcohol intake and late-stage promotion of breast cancer

Breast cancer risk in women rises with increasing alcohol intake and is widely assumed to be mediated by increased oestrogen concentrations. However, observations that mechanisms and risk are likely to differ between pre- and postmenopausal women suggest that the postmenopausal disease in particular, may involve a promoting role for concomitants of hyperinsulinaemia which is commonly associated with alcoholic cirrhosis of the liver. The MEDLINE database and ongoing studies were examined for clinical, epidemiological and laboratory data on; (a) alcohol-related increase in the incidence of breast cancer in relation to menopausal status, oestrogen concentrations and the oestrogen receptor (ER) status of the tumour; (b) activation of insulin-like growth factor 1 receptor (IGF1R) in mammary tissue by alcohol-related hyperinsulinaemia; (c) interaction between ER and IGF1R in breast cancer cell systems. Epidemiological association between alcohol intake and increased breast cancer risk is more clearly seen in postmenopausal than premenopausal women, and a significant risk is associated with intake of more than two drinks (over 30 g) daily over a period of years. Alcohol-related hyperinsulinaemia is reported to increase with increasing degrees of cirrhosis and damage to liver function. Laboratory evidence suggests that hyperinsulinaemia can stimulate expression of IGF1R in mammary tissue, and this protein is likely to have a crucial role in mitogenesis and transformation to an oestrogen-independent malignant phenotype. It is postulated that in women with a history of long-term intake of moderate quantities of alcohol, the concomitants of hyperinsulinaemia may help to stimulate progression in precancerous breast lesions in the years leading up to the menopause and may increase the risk of breast cancer manifesting after the menopause.

Risk of breast cancer in young women in relation to body size and weight gain in adolescence and early adulthood

Findings have been inconsistent on effects of adolescent body size and adult weight gain on risk of breast cancer in young women. These relations were examined in a population-based case control study of 1590 women less than 45 years of age newly diagnosed with breast cancer during 1990-1992 in three areas of the US and an age-matched control group of 1390 women. Height and weight were measured at interview and participants asked to recall information about earlier body size. Logistic regression was used to estimate the relative risk of breast cancer adjusted for other risk factors. Women who were either much heavier or lighter than average in adolescence or at age 20 were at reduced risk. Weight gain after age 20 resulted in reduced risk, but the effect was confined to early-stage and, more specifically, lower grade breast cancer. Neither the risk reduction nor the variation by breast cancer stage or grade was explained by the method of cancer detection or by prior mammography history. These findings suggest that relations between breast cancer risk in young women and body weight at different ages is complex and that the risk reduction with adult weight gain is confined to less aggressive cancers.

Do insulin-like growth factors mediate the effect of alcohol on breast cancer risk?

Despite a large number of epidemiologic studies demonstrating an increased risk of breast cancer in association with alcohol consumption, a causal relationship between alcohol intake and breast cancer risk remains to be determined. Several biological mechanisms have been proposed, but none of them explains well the features of the association, i.e. a modest increase in risk, a limited range of dose-response relationship and no further increase in risk among heavy drinkers. A new mechanism underlying a possible biological role of alcohol in breast cancer is proposed in this paper. Moderate consumption of alcohol increases the production of insulin-like growth factors (IGFs) by the liver and elevated IGFs via circulation stimulate or promote the development and/or growth of breast cancer. The effect of alcohol on IGF production declines among heavy drinkers as alcohol-caused liver-function damage results in no further increase in IGF production. Therefore, compared to moderate drinkers, heavy alcohol users do not have a higher risk of breast cancer.

Circulating tumor markers in breast cancer: accepted utilities and novel prospects

Detecting and/or monitoring changes in circulating tumor markers might assist in evaluating cancer risk, diagnosis, prognosis, or response to treatment. Several categories of circulating tumor markers have been investigated in breast cancer. These categories include classical tumor-associated antigens, such as CEA and CA 15-3, markers of tumor biology, including markers of angiogenesis, adhesion, and invasion, and antibody response to tumor-associated antigens such as HER2/neu and p53. We used a recently proposed Tumor Marker Utility Grading System to evaluate the use of several circulating tumor markers for different clinical utilities in breast cancer. While there are no tumor markers with established clinical utilities for most uses, tumor-associated antigens can be used for monitoring patients with metastatic disease. In addition, markers of tumor biology such as the circulating extracellular domain of HER2/neu might be useful in determining not only prognosis, but also response to specific treatments. However, further investigations are required to further assess the utility of individual tumor markers for specific clinical uses.

Adjuvant treatment and onset of menopause predict weight gain after breast cancer diagnosis

PURPOSE

Weight gain is common during the first year after breast cancer diagnosis. In this study, we examined clinical factors associated with body size at diagnosis and weight gain during the subsequent year.

PATIENTS AND METHODS

An inception cohort of 535 women with newly diagnosed locoregional breast cancer underwent anthropometric measurements at baseline and 1 year. Information was collected on tumor- and treatment-related variables, as well as diet and physical activity.

RESULTS

Mean age was 50.3 years; 57% of women were premenopausal. Mean baseline body mass index (weight [kg] divided by height [m] squared) was 25.5 kg/m2. Overall, 84.1% of the patients gained weight. Mean weight gain was 1.6 kg (95% confidence interval, 1.2 to 1.9 kg), 2.5 kg (95% confidence interval, 1.8 to 3.2 kg) in those receiving chemotherapy, 1.3 kg (95% confidence interval, 0.7 to 1.8 kg) in those receiving tamoxifen only, and 0.6 kg (95% confidence interval, 0.01 to 1.3 kg) in those receiving no adjuvant treatment. Menopausal status at diagnosis (P = .02), change in menopausal status over the subsequent year (P = .002), axillary nodal status (P = .009), and adjuvant treatment (P = .0002) predicted weight gain in univariate analysis. In multivariate analysis, onset of menopause and administration of chemotherapy were independent predictors of weight gain (all P < or = .05). Caloric intake decreased (P < .01) and physical activity increased (P < .05) during the year after diagnosis; these factors did not explain the observed weight gain.

CONCLUSION

Weight gain is common after breast cancer diagnosis; use of adjuvant chemotherapy and onset of menopause are the strongest clinical predictors of this weight gain.