Age-specific patterns of association between breast cancer and risk factors in black women, ages 20 to 39 and 40 to 54

Expression of p27 and c-Myc by immunohistochemistry in breast ductal cancers in African American women

OBJECTIVES

Proteins p27 and c-Myc are both key players in the cell cycle. While p27, a tumor suppressor, inhibits progression from G1 to S phase, c-Myc, a proto-oncogene, plays a key role in cell cycle regulation and apoptosis. The objective of our study was to determine the association between expression of c-Myc and the loss of p27 by immunohistochemistry (IHC) in the four major subtypes of breast cancer (BC) (Luminal A, Luminal B, HER2, and Triple Negative) and with other clinicopathological factors in a population of 202 African-American (AA) women.

MATERIALS AND METHODS

Tissue microarrays (TMAs) were constructed from FFPE tumor blocks from primary ductal breast carcinomas in 202 AA women. Five micrometer sections were stained with a mouse monoclonal antibody against p27 and a rabbit monoclonal antibody against c-Myc. The sections were evaluated for intensity of nuclear reactivity (1-3) and percentage of reactive cells; an H-score was derived from the product of these measurements.

RESULTS

Loss of p27 expression and c-Myc overexpression showed statistical significance with ER negative (p < 0.0001), PR negative (p < 0.0001), triple negative (TN) (p < 0.0001), grade 3 (p = 0.038), and overall survival (p = 0.047). There was no statistical significant association between c-Myc expression/p27 loss and luminal A/B and Her2 overexpressing subtypes.

CONCLUSION

In our study, a statistically significant association between c-Myc expression and p27 loss and the triple negative breast cancers (TNBC) was found in AA women. A recent study found that constitutive c-Myc expression is associated with inactivation of the axin 1 tumor suppressor gene. p27 inhibits cyclin dependent kinase2/cyclin A/E complex formation. Axin 1 and CDK inhibitors may represent possible therapeutic targets for TNBC.

Biology and Etiology of Young-Onset Breast Cancers among Premenopausal African American Women: Results from the AMBER Consortium

Background: African American (AA) women have higher incidence of aggressive, young-onset (<40 years) breast cancers. Young- and older-onset disease may have distinct tumor biologies and etiologies; however, studies investigating age differences among AA women have been rare and generally underpowered.Methods: We examined tumor characteristics and breast cancer risk factors associated with premenopausal young (<40) vs. older (≥40) AA women's breast cancer in the African American Breast Cancer Epidemiology and Risk Consortium (2,008 cases and 5,144 controls). Unconditional logistic regression models assessed heterogeneity of tumor biology and risk factor associations by age, overall, and by estrogen receptor status.Results: Premenopausal AA women <40 years had higher frequency of poorer-prognosis tumor characteristics compared with older women, including negative estrogen and progesterone receptor status, triple-negative subtype, higher grade, higher stage, and larger tumors. Adiposity (i.e., waist-to-hip ratio) and family history of breast cancer were more strongly associated with young-onset disease [case-control OR = 1.46, 95% confidence interval (CI) = 1.04-2.05; OR = 3.10, 95% CI = 2.08-4.63, respectively] compared with older-onset disease (OR = 1.11, 95% CI = 0.91-1.35; OR = 1.57, 95% CI = 1.26-1.94). Breastfeeding showed a slight inverse risk association among young women (OR = 0.70, 95% CI = 0.43-1.16). Oral contraceptive use was associated with increased risk regardless of age. Considering various cutoff points for young age (<40, <45, <50), age-related heterogeneity was greatest when <40 was used.Conclusions: Among premenopausal AA women, diagnosis before age 40 is associated with more aggressive breast tumor biology and some etiologic differences.Impact: Modifiable risk factors including breastfeeding, adiposity, and oral contraceptive use may be important targets for mitigating harms of young-onset breast cancer. Cancer Epidemiol Biomarkers Prev; 26(12); 1722-9. ©2017 AACR.

Breast cancer biologic and etiologic heterogeneity by young age and menopausal status in the Carolina Breast Cancer Study: a case-control study

BACKGROUND

Young-onset breast cancer (<40 years) is associated with worse prognosis and higher mortality. Breast cancer risk factors may contribute to distinct tumor biology and distinct age at onset, but understanding of these relationships has been hampered by limited representation of young women in epidemiologic studies and may be confounded by menopausal status.

METHODS

We examined tumor characteristics and epidemiologic risk factors associated with premenopausal women's and young women's breast cancer in phases I-III of the Carolina Breast Cancer Study (5309 cases, 2022 control subjects). Unconditional logistic regression was used to assess heterogeneity by age (<40 vs. ≥40 years) and menopausal status.

RESULTS

In both premenopausal and postmenopausal strata, younger women had more aggressive disease, including higher stage, hormone receptor-negative, disease as well as increased frequency of basal-like subtypes, lymph node positivity, and larger tumors. Higher waist-to-hip ratio was associated with reduced breast cancer risk among young women but with elevated risk among older women. Parity was associated with increased risk among young women and reduced risk among older women, while breastfeeding was more strongly protective for young women. Longer time since last birth was protective for older women but not for young women. In comparison, when we stratified by age, menopausal status was not associated with distinct risk factor or tumor characteristic profiles, except for progesterone receptor status, which was more commonly positive among premenopausal women.

CONCLUSIONS

Age is a key predictor of breast cancer biologic and etiologic heterogeneity and may be a stronger determinant of heterogeneity than menopausal status. Young women's breast cancer appears to be etiologically and biologically distinct from that among older women.

Body fatness throughout the life course and the incidence of premenopausal breast cancer

BACKGROUND

The role of body fatness in the aetiology of breast cancer is complex. We evaluated the independent and synergistic effects of body fatness, at different stages throughout a woman's life course, on premenopausal breast cancer risk.

METHODS

Premenopausal participants of the Nurses' Health Study II (NHSII) were followed from 1991 up to 2009. Body fatness factors including birthweight, somatotype (a 9-level pictogram with level 1 being the leanest) at ages 5 and 10 years and body mass index (BMI) at age 18 were collected at baseline. Current BMI was updated biennially. Multivariate Cox regression models were used to evaluate the association between each body fatness factor as well as cross-classification of all factors and the incidence of breast cancer.

RESULTS

Based on 1574 incident premenopausal breast cancer cases and 1 133 893 person-years of follow-up, a lower incidence was associated with lower birthweight: hazard ratio (HR) [95% confidence interval (CI)] = 0.74 (0.58-0.95) for <2.5kg vs 3.9+kg, P for trend < 0.001; higher somatotype at age 5: HR=0.57 (95% CI 0.44-0.73) for 5-9 vs 1, P fortrend < 0.0001]; and at age 10: HR=0.61 (95% CI 0.49-0.75) for 5-9 vs 1, P for trend < 0.0001]; and BMI at age 18: HR=0.67 (95% 0.47-0.95) for ≥ 27.5 kg/m² vs < 18.5 kg/m², P for trend = 0.009], after adjusting for age and body fatness measures earlier in life and other risk factors, respectively. No significant interaction between body fatness measures was found. Women with the lowest birthweight, the highest somatotype at ages 5 and 10 and the highest BMI at age 18 and currently had a 72% (95% CI 54%-83%) lower incidence of invasive premenopausal breast cancer than women with the opposite extreme of each body fatness indicator.

CONCLUSION

The lowest incidence of premenopausal breast cancer was associated with the lowest birthweight and the highest childhood, adolescent and early adult body fatness.

Population-specific prognostic models are needed to stratify outcomes for African-Americans with diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) demonstrates significant racial differences in age of onset, stage, and survival. To examine whether population-specific models improve prediction of outcomes for African-American (AA) patients with DLBCL, we utilized Surveillance, Epidemiology, and End Results data and compared stratification by the international prognostic index (IPI) in general and AA populations. We also constructed and compared prognostic models for general and AA populations using multivariable logistic regression (LR) and artificial neural network approaches. While the IPI adequately stratified outcomes for the general population, it failed to separate AA DLBCL patients into distinct risk groups. Our AA LR model identified age ≥ 55 (odds ratio 0.45, [95% CI: 0.36, 0.56], male sex (0.75, [0.60, 0.93]), and stage III/IV disease (0.43, [0.34, 0.54]) as adverse predictors of 5-year survival for AA patients. In addition, general-population prognostic models were poorly calibrated for AAs with DLBCL, indicating a need for validated AA-specific prognostic models.

Racial and ethnic disparities in the impact of obesity on breast cancer risk and survival: a global perspective

Obesity is a global concern, affecting both developed and developing countries. Although there are large variations in obesity and breast cancer rates worldwide and across racial/ethnic groups, most studies evaluating the impact of obesity on breast cancer risk and survival have been conducted in non-Hispanic white women in the United States or Europe. Given the known racial/ethnic differences in tumor hormone receptor subtype distribution, obesity prevalence, and risk factor profiles, we reviewed published data for women of African, Hispanic, and Asian ancestry in the United States and their countries of origin. Although the data are limited, current evidence suggests a stronger adverse effect of obesity on breast cancer risk and survival in women of Asian ancestry. For African Americans and Hispanics, the strength of the associations appears to be more comparable to that of non-Hispanic whites, particularly when accounting for subtype and menopausal status. Central obesity seems to have a stronger impact in African-American women than general adiposity as measured by body mass index. International data from countries undergoing economic transition offer a unique opportunity to evaluate the impact of rapid weight gain on breast cancer. Such studies should take into account genetic ancestry, which may help elucidate differences in associations between ethnically admixed populations. Overall, additional large studies that use a variety of adiposity measures are needed, because the current evidence is based on few studies, most with limited statistical power. Future investigations of obesity biomarkers will be useful to understand possible racial/ethnic biological differences underlying the complex association between obesity and breast cancer development and progression.

Energy-Related Indicators and Breast Cancer Risk among White and Black Women

Energy-related indicators, including physical activity, energy intake, body mass index (BMI) and adult weight change, have been linked to breast cancer risk. Very few studies of these associations have been conducted among black women, therefore we used the Nashville Breast Health Study (NBHS) to determine whether similar effects were seen in black and white women. The NBHS is a population-based case-control study of breast cancer among women age 25 to 75 years conducted between 2001 and 2010 in and around the Nashville Metropolitan area. Telephone interviews and self-administered food frequency questionnaires were completed with 2,614 incident breast cancer cases ascertained through hospitals and the statewide cancer registry, and 2,306 controls selected using random digit dialing. Among premenopausal white and black women, there was little effect of adult exercise or other energy-related indicators on breast cancer risk, regardless of tumor estrogen receptor (ER) status. The beneficial effect of adult exercise on postmenopausal breast cancer appeared to be comparable between white and black women (highest tertile relative to none - white odds ratio [OR] 0.8, 95% confidence interval [CI] 0.6-1.0, p for trend=0.05; black OR 0.7, 95% CI 0.4-1.1, p for trend=0.07); however, among black women the reduction was limited to those with ER-positive disease. White and black women should be encouraged to engage in more physical activity to reduce their risk of postmenopausal breast cancer.

Obesity, body fat distribution, and risk of breast cancer subtypes in African American women participating in the AMBER Consortium

African American (AA) women are more likely than white women to be obese and to be diagnosed with ER- and triple-negative (TN) breast cancer, but few studies have evaluated the impact of obesity and body fat distribution on breast cancer subtypes in AA women. We evaluated these associations in the AMBER Consortium by pooling data from four large studies. Cases were categorized according to hormone receptor status as ER+, ER-, and TN (ER-, PR-, and HER2-) based on pathology data. A total of 2104 ER+ cases, 1070 ER- cases (including 491 TN cases), and 12,060 controls were included. Odds ratios (OR) and 95 % confidence intervals (CI) were computed using logistic regression, taking into account breast cancer risk factors. In postmenopausal women, higher recent (most proximal value to diagnosis/index date) BMI was associated with increased risk of ER+ cancer (OR 1.31; 95 % CI 1.02-1.67 for BMI ≥ 35 vs. <25 kg/m(2)) and with decreased risk of TN tumors (OR 0.60; 95 % CI 0.39-0.93 for BMI ≥ 35 vs. <25). High young adult BMI was associated with decreased premenopausal ER+ cancer and all subtypes of postmenopausal cancer, and high recent waist-to-hip ratio with increased risk of premenopausal ER+ tumors (OR 1.35; 95 % CI 1.01-1.80) and all tumor subtypes combined in postmenopausal women (OR 1.26; 95 % CI 1.02-1.56). The impact of general and central obesity varies by menopausal status and hormone receptor subtype in AA women. Our findings imply different mechanisms for associations of adiposity with TN and ER+ breast cancers.

Body fatness and breast cancer risk in women of African ancestry

Background

Obesity has been shown to be inversely associated with breast cancer risk in premenopausal women, while increasing risk in postmenopausal women. However, the current evidence is largely based on studies in Caucasian populations. Associations in women of African ancestry (AA), who have a higher prevalence of obesity, have been evaluated in few studies and results suggest different effects.

Methods

We evaluated the impact of body size, body fat distribution, and body composition on breast cancer risk among AA women (978 cases and 958 controls) participating in the Women’s Circle of Health Study, a multi-site case–control study in New York City (NYC) and New Jersey (NJ). Cases were newly diagnosed with histologically confirmed ductal carcinoma in situ or invasive breast cancer, age 20–75 yrs. In NYC, cases were recruited through hospitals with the largest referral patterns for AA women and controls through random digit dialing (RDD). In NJ, cases were identified in seven counties in NJ thorough the NJ State Cancer Registry, and controls through RDD and community-based recruitment. During in-person interviews, questionnaires were administered and detailed anthropometric measurements were obtained. Body composition was assessed by bioelectrical impedance analysis.

Results

BMI did not have a major impact on pre- or post-menopausal breast cancer, but was significantly associated with reduced risk of ER-/PR- tumors among postmenopausal women (OR: 0.37; 95% CI: 0.15-0.96 for BMI > 30 vs. BMI < 25). Furthermore, increased premenopausal breast cancer risk was found for higher waist and hip circumferences after adjusting for BMI, with ORs of 2.25 (95% CI: 1.07-4.74) and 2.91 (95% CI: 1.39-6.10), respectively, comparing the highest vs. lowest quartile. While ORs for higher fat mass and percent body fat among postmenopausal women were above one, confidence intervals included the null value.

Conclusions

Our study suggests that in AA women BMI is generally unrelated to breast cancer. However, higher waist and hip circumferences were associated with increased pre-menopausal breast cancer risk, while general obesity was associated with decreased risk of ER-/PR- tumors. Larger studies are needed to confirm findings and to evaluate the impact of obesity on breast cancer subtypes.

Body size in early life and breast cancer risk in African American and European American women

PURPOSE

There is growing evidence that body size in early life influences lifetime breast cancer risk, but little is known for African American (AA) women.

METHODS

We evaluated body size during childhood and young adulthood and breast cancer risk among 1,751 cases [979 AA and 772 European American (EA)] and 1,673 controls (958 AA and 715 EA) in the Women's Circle of Health Study. Odds ratio (OR) and 95 % confidence intervals (CI) were computed using logistic regression models while adjusting for potential covariates.

RESULTS

Among AA women, being shorter at 7-8 years compared to peers was associated with increased postmenopausal breast cancer risk (OR 1.68, 95 % CI 1.02-2.74), and being heavier at menarche with decreased postmenopausal breast cancer risk, although of borderline significance (OR 0.45, 95 % CI 0.20-1.02). For EA women, being shorter from childhood through adolescence, particularly at menarche, was associated with reduced premenopausal breast cancer risk (OR 0.55, 95 % CI 0.31-0.98). After excluding hormone replacement therapy users, an inverse association with postmenopausal breast cancer was found among EA women reporting to be heavier than their peers at menarche (OR 0.18, 95 % CI 0.04-0.79). The inverse relationship between BMI at age 20 and breast cancer risk was stronger and only statistically significant in EA women. No clear association with weight gain since age 20 was found.

CONCLUSIONS

Findings suggest that the impact of childhood height on breast cancer risk may differ for EA and AA women and confirm the inverse association previously reported in EA populations with adolescent body fatness, in AA women.

The role of anthropometric and nutritional factors on breast cancer risk in African-American women

OBJECTIVE

While the role of nutrition, physical activity and body size on breast cancer risk has been extensively investigated, most of these studies were conducted in Caucasian populations. However, there are well-known differences in tumour biology and the prevalence of these factors between African-American and Caucasian women. The objective of the present paper was to conduct a review of the role of dietary factors, anthropometry and physical activity on breast cancer risk in African-American women.

DESIGN

Twenty-six research articles that presented risk estimates on these factors in African-American women and five articles involving non-US black women were included in the current review.

SETTING

Racial disparities in the impact of anthropometric and nutritional factors on breast cancer risk.

SUBJECTS

African-American and non-US black women.

RESULTS

Based on the few studies that presented findings in African-American women, an inverse association with physical activity was found for pre- and postmenopausal African-American women, while the association for anthropometric and other dietary factors, such as alcohol, was unclear. Studies assessing the effect by molecular subtypes in African-American women were too few and based on sample sizes too small to provide definitive conclusions.

CONCLUSIONS

The effect of certain nutrition and lifestyle factors on breast cancer in African-American women is not starkly distinct from those observed in white women. However, there is an enormous need for further research on this minority group to obtain more confirmatory findings.

A review of body size and breast cancer risk in Hispanic and African American women

Obesity is an epidemic in the United States, especially among Hispanics and African Americans. Studies of obesity and breast cancer risk have been conducted primarily in non-Hispanic whites. There have been few studies of the association between body mass index (BMI) or weight gain and the risk of breast cancer in minorities, and the results have been inconsistent. Because most studies are conducted primarily in non-Hispanic whites, the etiology of breast cancer in minorities is not well understood. The authors of the current report reviewed the literature on the association between obesity, weight, and weight gain and breast cancer in minorities using a combination of the Medical Subject Heading (MeSH) terms "obesity," "body mass index," "weight," "weight gain," "Hispanic," and "African American." Only publications in English and with both risk estimates and 95% confidence intervals were considered. Forty-five studies of body size and breast cancer risk in non-Hispanic whites were identified. After an exhaustive search of the literature, only 3 studies of body size and breast cancer were conducted in Hispanic women were identified, and only 8 such studies in African American women were identified. The results were inconsistent in both race/ethnicity groups, with studies reporting positive, inverse, and null results. Thus, as obesity rates among Hispanics and African Americans continue to rise, there is an urgent need to identify the roles that both obesity and adult weight gain play in the development of breast cancer in these minorities. Additional studies are needed to provide more understanding of the etiology of this disease and to explain some of the disparities in incidence and mortality.

Adult body size, hormone receptor status, and premenopausal breast cancer risk in a multiethnic population: the San Francisco Bay Area breast cancer study

Large body size has been associated with a reduced risk of premenopausal breast cancer in non-Hispanic white women. Data on other racial/ethnic populations are limited. The authors examined the association between premenopausal breast cancer risk and adult body size in 672 cases and 808 controls aged ≥35 years from a population-based case-control study conducted in 1995-2004 in the San Francisco Bay Area (Hispanics: 375 cases, 483 controls; African Americans: 154 cases, 160 controls; non-Hispanic whites: 143 cases, 165 controls). Multivariate adjusted odds ratios and 95% confidence intervals were calculated using unconditional logistic regression. Height was associated with increased breast cancer risk (highest vs. lowest quartile: odds ratio = 1.77, 95% confidence interval: 1.23, 2.53; P(trend) < 0.01); the association did not vary by hormone receptor status or race/ethnicity. Body mass index (measured as weight (kg) divided by height (m) squared) was inversely associated with risk in all 3 racial/ethnic groups, but only for estrogen receptor- and progesterone receptor-positive tumors (body mass index ≥30 vs. <25: odds ratio = 0.42; 95% confidence interval: 0.29, 0.61). Other body size measures (current weight, body build, adult weight gain, young adult weight and body mass index, waist circumference, and waist-to-height ratio) were similarly inversely associated with risk of estrogen receptor- and progesterone receptor-positive breast cancer but not estrogen receptor- and progesterone receptor-negative disease. Despite racial/ethnic differences in body size, inverse associations were similar across the 3 racial/ethnic groups when stratified by hormone receptor status.

A case-control study of body mass index and breast cancer risk in white and African-American women

OBJECTIVE

Large body size has been associated with decreased risk of breast cancer in premenopausal women but with increased risk in postmenopausal women. Limited information is available about African-American women and differences by estrogen and progesterone receptor status.

METHODS

We analyzed data from the Women's Contraceptive and Reproductive Experiences Study among 3,997 white and African-American breast cancer case patients diagnosed in 1994 to 1998 and 4,041 control participants ages 35 to 64 years. We calculated multivariate odds ratios (OR) as measures of relative risk of breast cancer associated with self-reported body mass index (BMI) at age 18 and 5 years before diagnosis (recent BMI).

RESULTS

Risk tended to decrease with increasing BMI at age 18 years in all women [OR(BMI > or = 25 kg/m(2) versus < 20 kg/m(2)) = 0.76; 95% confidence interval (CI), 0.63-0.90; P(trend) = 0.005] and with recent BMI in premenopausal women (OR(BMI > or = 35 kg/m(2) versus < 25 kg/m(2)) = 0.81; 95% CI, 0.61-1.06; P(trend) = 0.05), unmodified by race. Among postmenopausal white but not African-American women, there was an inverse relation between recent BMI and risk. High recent BMI was associated with increased risk of estrogen receptor- and progesterone receptor-positive tumors among postmenopausal African-American women (OR(BMI > or = 35 kg/m(2) versus < 25 kg/m(2)) = 1.83; 95% CI, 1.08-3.09; P(trend) = 0.03).

CONCLUSION

Among women at age 35 to 64 years, BMI at age 18 years is inversely associated with risk of breast cancer, but association with recent BMI varies by menopause status, race, and hormone receptor status.

IMPACT

Our findings indicate that studies of BMI and breast cancer should consider breast cancer subtypes.

Racial differences in the association between body mass index and serum IGF1, IGF2, and IGFBP3

African-American (AA) race/ethnicity, lower body mass index (BMI), and higher IGF1 levels are associated with premenopausal breast cancer risk. This cross-sectional analysis investigated whether BMI or BMI at age 21 years contributes to racial differences in IGF1, IGF2, IGF-binding protein 3 (IGFBP3), or free IGF1. Participants included 816 white and 821 AA women between ages 40 and 79 years across a wide BMI range (18.5-40 kg/m(2)). Compared with white women, AA women had higher mean IGF1 (146.3 vs 134.4 ng/ml) and free IGF1 (0.145 vs 0.127) levels, and lower IGF2 (1633.0 vs 1769.3 ng/ml) and IGFBP3 (3663.3 vs 3842.5 ng/ml) levels (all P<0.01; adjusted for age, height, BMI, BMI at age 21 years, and menopausal status). Regardless of race, IGF1 and free IGF1 levels rose sharply as BMI increased to 22-24 kg/m(2), and then declined thereafter, while IGF2 and IGFBP3 levels tended to rise with BMI. In contrast, BMI at age 21 years was inversely associated with all IGF levels, but only among white women (P-interaction=0.01). With the decline in IGF1 with BMI at age 21 years among whites, racial differences in IGF1 significantly increased among women who were obese in early adulthood. In summary, BMI was associated with IGF1 levels regardless of race/ethnicity, while obesity during childhood or young adulthood may have a greater impact on IGF1 levels among white women. The effects of obesity throughout life on the IGF axis and racial differences in breast cancer risk require study.

Body size and breast cancer in a black population--the Barbados National Cancer Study

OBJECTIVE

To evaluate the relationship between body size and incident breast cancer in an African-origin Caribbean population.

METHODS

This investigation is based on 222 incident breast cancer cases and 454 controls from the Barbados National Cancer Study (BNCS) in whom body size variables that included height, weight, body-mass index (BMI), waist and hip circumferences (WC, HC), and waist-hip ratio (WHR) were compared. Multivariate-adjusted logistic regression analyses were performed and the findings are presented as odds ratios (ORs) with 95% confidence intervals (CI).

RESULTS

Although 33% of cases and 39% of controls were obese (BMI > or = 30 kg/m(2)), BMI was not found to be a significant predictor of breast cancer in the multivariate analyses. Tall stature increased risk among women > or =50 years (OR = 2.16, 95% CI (1.02, 4.58)), and a dual effect with age was suggested for both WC and WHR (decreased risk for those aged < or =50 years; increased risk among those > or =50 years).

CONCLUSIONS

Body size appears to influence the risk of breast cancer in this population of African origin. The BNCS data suggest that a few, but not all body size factors play a role in breast cancer risk, and that age may affect these relationships.

A case-control study of oral contraceptive use and incident breast cancer

Oral contraceptive (OC) use has been linked to increased risk of breast cancer, largely on the basis of studies conducted before 1990. In the Case-Control Surveillance Study, a US hospital-based case-control study of medication use and cancer, the authors assessed the relation of OC use to breast cancer risk among 907 case women with incident invasive breast cancer (731 white, 176 black) and 1,711 controls (1,152 white, 559 black) interviewed from 1993 to 2007. They evaluated whether the association differed by ethnicity or tumor hormone receptor status. After control for breast cancer risk factors, the multivariable odds ratio for 1 year or more of OC use, relative to less than 1 year of use, was 1.5 (95% confidence interval: 1.2, 1.8). The estimates were similar within age strata (<50 years and >or= 50 years). The odds ratios were larger for use within the previous 10 years, long-duration use, and black ethnicity, but these differences were not statistically significant. The association of OC use with breast cancer risk did not differ according to the estrogen or progestogen receptor status of the tumor. These results suggest that OC use is associated with an increased risk of breast cancer diagnosed in recent years.

Energy balance, physical activity, and cancer risk

This chapter posits that cancer is a complex and multifactorial process as demonstrated by the expression and production of key endocrine and steroid hormones that intermesh with lifestyle factors (physical activity, body size, and diet) in combination to heighten cancer risk. Excess weight has been associated with increased mortality from all cancers combined and for cancers of several specific sites. The prevalence of obesity has reached epidemic levels in many parts of the world; more than 1 billion adults are overweight with a body mass index (BMI) exceeding 25. Overweight and obesity are clinically defined indicators of a disease process characterized by the accumulation of body fat due to an excess of energy intake (nutritional intake) relative to energy expenditure (physical activity). When energy intake exceeds energy expenditure over a prolonged period of time, the result is a positive energy balance (PEB), which leads to the development of obesity. This physical state is ideal for intervention and can be modulated by changes in energy intake, expenditure, or both. Nutritional intake is a modifiable factor in the energy balance-cancer linkage primarily tested by caloric restriction studies in animals and the effect of energy availability. Restriction of calories by 10 to 40% has been shown to decrease cell proliferation, increasing apoptosis through anti-angiogenic processes. The potent anticancer effect of caloric restriction is clear, but caloric restriction alone is not generally considered to be a feasible strategy for cancer prevention in humans. Identification and development of preventive strategies that "mimic" the anticancer effects of low energy intake are desirable. The independent effect of energy intake on cancer risk has been difficult to estimate because body size and physical activity are strong determinants of total energy expenditure. The mechanisms that account for the inhibitory effects of physical activity on the carcinogenic process are reduction in fat stores, activity related changes in sex-hormone levels, altered immune function, effects in insulin and insulin-like growth factors, reduced free radical generation, and direct effect on the tumor. Epidemiologic evidence posits that the cascade of actions linking overweight and obesity to carcinogenesis are triggered by the endocrine and metabolic system. Perturbations to these systems result in the alterations in the levels of bioavailable growth factors, steroid hormones, and inflammatory markers. Elevated serum concentrations of insulin lead to a state of hyperinsulinemia. This physiological state causes a reduction in insulin-like growth factor-binding proteins and promotes the synthesis and biological activity of insulin-like growth factor (IGF)-I, which regulates cellular growth in response to available energy and nutrients from diet and body reserves. In vitro studies have clearly established that both insulin and IGF-I act as growth factors that promote cell proliferation and inhibit apoptosis. Insulin also affects on the synthesis and biological availability of the male and female sex steroids, including androgens, progesterone, and estrogens. Experimental and clinical evidence also indicates a central role of estrogens and progesterone in regulating cellular differentiation, proliferation, and apoptosis induction. Hyperinsulinemia is also associated with alterations in molecular systems such as endogenous hormones and adipokines that regulate inflammatory responses. Obesity-related dysregulation of adipokines has the ability to contribute to tumorigenesis and tumor invasion via metastatic potential. Given the substantial level of weight gain in industrialized countries in the last two decades, there is great interest in understanding all of the mechanisms by which obesity contributes to the carcinogenic process. Continued focus must be directed to understanding the various relationships between specific nutrients and dietary components and cancer cause and prevention. A reductionist approach is not sufficient for the basic biological mechanisms underlying the effect of diet and physical activity on cancer. The joint association between energy balance and cancer risk are hypothesized to share the same underlying mechanisms, the amplification of chemical mediators that modulate cancer risk depending on the responsiveness to those hormones to the target tissue of interest. Disentangling the connection between obesity, the insulin-IGF axis, endogenous hormones, inflammatory markers, and their molecular interaction is vital.

Risk factors for breast cancer in a black population--the Barbados National Cancer Study

The Barbados National Cancer Study (BNCS) is a nationwide case-control study investigating environmental and genetic factors for breast cancer (BC) in a predominantly African-origin population with similar ancestry as African-Americans. This report evaluates associations of incident BC in the BNCS to various factors, including demographic, anthropometric, reproductive and family history variables, not investigated previously in this population. The BNCS included 241 incident BC cases and 481 age-matched female controls, with mean ages of 57 and 56 years, respectively. In addition to a reported family history of BC in a close relative [odds ratios (OR) = 3.74, 95% CI (1.41, 9.90) in a parent; OR = 3.26 (1.47, 7.21) in a sibling], other factors associated with BC were older age at first full-term pregnancy [OR = 1.04 (1.00, 1.07)] and having a history of benign breast disease [OR = 1.88 (1.19, 2.99)]. Increased parity reduced the risk of BC [OR = 0.34 (0.15, 0.77) among those with >or=3 children]. The reproductive patterns of African-Barbadian (AB) women tended to differ from those of African-American (AA) women (later age of menarche, earlier age at first pregnancy, higher frequency of lactation and infrequent use of exogenous hormones) and could help to explain their considerably lower postmenopausal incidence of BC. The relationship between reported family history and BC, combined with the associations noted for several reproductive and other variables, supports the genetic and environmental contributions to BC, which may vary in populations across the African diaspora. Further investigations of other populations may clarify these issues.

Oral contraceptive use as a risk factor for premenopausal breast cancer: a meta-analysis

OBJECTIVE

To perform a meta-analysis of case-control studies that addressed whether prior oral contraceptive (OC) use is associated with premenopausal breast cancer.

METHODS

We searched the MEDLINE and PubMed databases and bibliography reviews to identify case-control studies of OCs and premenopausal breast cancer published in or after 1980. Search terms used included breast neoplasms, oral contraceptives, contraceptive agents, and case-control studies. Studies reported in all languages were included. Thirty-four studies were identified that met inclusion criteria. Two reviewers extracted data from original research articles or additional data provided by study authors. We used the DerSimonian-Laird method to compute pooled odds ratios (ORs) and confidence intervals (CIs) and the Mantel-Haenszel test to assess association between OC use and cancer.

RESULTS

Use of OCs was associated with an increased risk of premenopausal breast cancer in general (OR, 1.19; 95% CI, 1.09-1.29) and across various patterns of OC use. Among studies that provided data on nulliparous and parous women separately, OC use was associated with breast cancer risk in both parous (OR, 1.29; 95% CI, 1.20-1.40) and nulliparous (OR, 1.24; 95% CI, 0.92-1.67) women. Longer duration of use did not substantially alter risk in nulliparous women (OR, 1.29; 95% CI, 0.85-1.96). Among parous women, the association was stronger when OCs were used before first full-term pregnancy (FFTP) (OR, 1.44; 95% CI, 1.28-1.62) than after FFTP (OR, 1.15; 95% CI, 1.06-1.26). The association between OC use and breast cancer risk was greatest for parous women who used OCs 4 or more years before FFTP (OR, 1.52; 95% CI, 1.26-1.82).

CONCLUSION

Use of OCs is associated with an increased risk of premenopausal breast cancer, especially with use before FFTP in parous women.

Breast Cancer Risk Estimates for Relatives of White and African American Women With Breast Cancer in the Women's Contraceptive and Reproductive Experiences Study

Purpose

Family history is a well-recognized risk factor for breast cancer. Familial aggregation and segregation analyses have estimated breast cancer risk based on family history primarily for white women; such information is limited for African American (AA) women. The purpose of this report is to update breast cancer risk estimates associated with a family history of breast cancer for white and AA women.

Methods

We used family cancer history from 2,676 white and 1,525 AA women with breast cancer (probands) in the population-based National Institute of Child Health and Human Development's Women's Contraceptive and Reproductive Experiences (CARE) Study to estimate age-specific breast cancer risks in their first degree adult female relatives. Cumulative hazard curves were calculated for relatives of all probands using Cox proportional hazards models, and were stratified by the proband's race and age at diagnosis and number of relatives affected.

Results

Breast cancer risks for white and AA women with a family history of the disease are similar through age 49 years, but diverge afterwards, with higher risks by age 79 in white women than in AA women (17.5% [SE, 0.9%] v 12.2% [SE, 1.1%]; P < .001). These risks increase as the number of affected first degree relatives increases, reaching 25.2% (SE, 3.4%) and 16.9% (SE, 4.0%) in white and AA women with more than one affected relative, respectively (P = .3).

Conclusion

We found age-related racial differences in breast cancer risk in women with a family history of breast cancer and have updated risk estimates for white and AA women for clinical use.

Risk factors for fatal breast cancer in African-American women and White women in a large US prospective cohort

African-American women have a higher lifetime risk of fatal breast cancer than do White women. Recent studies suggest that breast cancer risk factors may vary by race. The authors examined risk factors for fatal breast cancer in postmenopausal African-American women and White women in a large US prospective cohort. In 1982, 21,143 African-American women and 409,093 White women in the Cancer Prevention Study II completed a questionnaire on reproductive, medical, anthropometric, and demographic factors. During a 20-year follow-up, 257 deaths from breast cancer occurred among African-American women and 4,265 among Whites. Cox proportional hazards modeling was used to calculate multivariate-adjusted rate ratios, stratified by race. Higher body mass index, taller height, and physical inactivity were associated with increased breast cancer mortality rates in both groups. A college education was associated with higher mortality from breast cancer only in Africa-American women (hazard ratio = 1.62, 95% confidence interval: 1.13, 2.30; p(trend) = 0.01, vs. less than a high school education). Most other risk factors were associated with breast cancer rates similarly in both groups. With few exceptions, established breast cancer risk factors were similarly associated with risk of death from breast cancer among African-American women and White women.

Barriers to minority participation in breast carcinoma prevention trials

BACKGROUND

Breast carcinoma prevention trials must recruit large cohorts of women who have an above-average risk of developing breast carcinoma. Recruitment for the Study of Tamoxifen and Raloxifene (STAR) trial required volunteers to complete a risk assessment questionnaire form (RAF). Women whose estimated risk of developing breast carcinoma in the next 5 years was > or = 1.67% based on the Gail model were invited to participate in STAR. Less than 4% of participants in the previously conducted P1 (tamoxifen vs. placebo) trial were minority women. We, therefore, studied barriers to minority participation in STAR among black, white, and Hispanic women who completed an RAF.

METHODS

The authors analyzed the association of Gail model risk factors, education, and insurance with race/ethnicity using chi-square tests and two-sided P values. They developed logistic regression models of trial eligibility, controlling for the Gail model risk factors, education, and insurance status.

RESULTS

Among 823 women who completed an RAF, white women were 10 times as likely as Hispanic women and 45 times as likely as black women to be eligible for STAR. Age at first birth (P = 0.04), having an affected first-degree relative (P < 0.0001), having had a biopsy (P < 0.0001), education (P < 0.0001), and insurance status (P < 0.0001) varied by race/ethnicity. All variables except insurance status were associated with eligibility when race was excluded from the model. In a model that included race/ethnicity, the same factors remained statistically significant.

CONCLUSIONS

These findings suggested that both the race/ethnicity adjustment and socioeconomic factors were barriers to eligibility for and contribute to low minority participation in breast cancer prevention trials.

Body mass index and breast cancer risk in African American women

PURPOSE

Studies of the relationship between body mass index (BMI) and breast cancer in African American women have been few. We conducted a case-control study to examine whether BMI is associated with risk of breast cancer in this population.

METHODS

Cases were 304 women diagnosed with breast cancer at the ages of 20 to 64 years. Controls were 305 women without a history of breast cancer. Telephone interviews were conducted to collect data on history of exposure to various factors at or before the date of diagnosis in cases or equivalent date in controls (reference date). Using logistic regression, we compared cases and controls in BMI at age 18, BMI at the reference date, and change in BMI between the two dates.

RESULTS

Using BMI at reference date, we found an odds ratio (OR) of 1.75 (95% confidence interval [CI], 1.02-3.02) and 2.32 (95% CI, 1.33-4.03) for women with BMI of 25 to 29.9 and 30 or higher, respectively, compared with women having BMI lower than 25. The corresponding OR estimates for BMI at age 18 were not significantly different from the unity. The average annual change in BMI between age 18 and date of diagnosis or reference date was associated with breast cancer risk, as shown that more BMI change tended to increase breast cancer risk compared with the baseline quartile of change. When data were analyzed by menopausal status, the association was found for both post-menopausal and pre-menopausal tumors for BMI at reference date but not for BMI at age 18. There was a higher risk for more annual BMI change compared with the baseline for both pre-menopausal and post-menopausal women.

CONCLUSION

Our results suggest that BMI at reference date and change in BMI were associated with increased risk of breast cancer in African American women, and the association might be found for both post-menopausal and pre-menopausal tumors.

Breast Cancer in African‐American Women

African-American women face a lower risk of being diagnosed with breast cancer as compared to Caucasian-American women, yet they paradoxically face an increased breast cancer mortality hazard. An increased incidence rate for early-onset disease has also been documented. This manuscript review summarizes the socioeconomic, environmental, genetic, and possible primary tumor biologic factors that may explain these disparities.

Dual effect of parity on breast cancer risk in African-American women

BACKGROUND

In the United States, breast cancer incidence is higher among African-American women than among white women before age 45 but lower at older ages. To explore whether differences in childbearing patterns can explain this observation, we assessed the relation of several childbearing variables to breast cancer risk in a large prospective cohort study of U.S. African-American women.

METHODS

Black Women's Health Study participants were enrolled in 1995 and were followed by mailed questionnaires every 2 years (in 1997 and 1999). Of the 64,500 women enrolled, 56,725 (88%) completed at least one of the follow-up questionnaires. During 214,862 person-years of follow-up, participants reported 349 breast cancers, of which 128 were among women younger than 45 years and 221 were among women aged 45-70 years. Incidence rate ratios (IRRs) with 95% confidence intervals (CIs) were derived from age-stratified Cox regression models that adjusted for each of the childbearing variables (parity, age at first birth, and time since last birth).

RESULTS

Compared with primiparity, high parity was associated with an increased risk of breast cancer among women younger than 45 years (IRR for four or more births = 2.4, 95% CI = 1.1 to 5.1) and a decreased risk among women aged 45 years and older (IRR = 0.5, 95% CI = 0.3 to 0.9). The IRR for late age at first birth compared with early age was 2.5 (95% CI = 1.1 to 5.8) among the younger women and was not elevated among older women. We found no statistically significant association of time since last birth with breast cancer risk among either younger or older women.

CONCLUSIONS

Parity has a dual association with breast cancer risk in African-American women; among women younger than 45 years, parity is associated with an increased risk and among women 45 years and older it is associated with a decreased risk. This dual effect may explain some of the observed differences in breast cancer incidence rates among African-American and white women.

Environmental risk factors for breast cancer among African-American women

There are few unequivocably established environmental carcinogens for breast cancer in women. Nevertheless, environmental factors are believed to explain much of the international variation in breast cancer risk and possibly differences among racial/ethnic groups. Along with lifestyle, some adverse exposures may be higher in minority racial/ethnic groups and in underserved populations that experience higher ambient contamination. Associations have been found between environmental agents and breast cancer in subgroups of women who can be identified by common susceptibility traits as well as by timing of exposures at certain milestones of reproductive life. Susceptibility can be defined by social, environmental, and genetic modalities-factors that may predominate in certain racial/ethnic groups but that also transcend racial/ethnic boundaries. For example, genes involved in transcription and estrogen metabolism have rapid variants that are more prevalent among African-Americans, yet risk accompanying metabolic changes from these genes will prevail in all racial/ethnic groups. Lack of reliable exposure assessment remains a principal obstacle to elucidating the role of environmental exposures in breast cancer. Resources must be identified and consolidated that will enable scientists to improve exposure assessment and to assemble studies of sufficient size to address questions regarding exposure, susceptibility, and vulnerability factors in breast cancer. Breast cancer studies should be expanded to examine combinations of chemicals as well as competing or complementary exposures such as endogenous hormones, dietary intake, and behavioral factors.

Breast cancer risk assessment models: applicability to African-American women

BACKGROUND

Mortality rates are higher among African-American women with breast cancer than they are among white women. This population subset can benefit from available risk reduction strategies. Optimal public health gains from chemoprevention strategies depend on the ability to assess accurately the risk for the individual. However, it is not known if existing breast cancer prediction models are accurate predictors of the disease among African-American women.

METHODS

Literature was reviewed for breast cancer risk prediction models and their validation studies. Reported data were also reviewed regarding the strength of established breast cancer risk factors for African-American women.

RESULTS

The two currently accepted breast cancer risk assessment models, the Gail Model and the Claus Model, were designed primarily to provide risk assessments for white women. Neither model has been validated in African-American women. Reported data are inconsistent regarding the prevalence and strength of risk factors included in these models.

CONCLUSIONS

Efforts should be made to validate existing risk assessment models in African-American women and future research should be directed at the identification of more reliable risk assessment features.

Reproductive factors and breast cancer risk. Do they differ according to age at diagnosis?

Studies yielding results on risk factors stratified by age at diagnosis or menopausal status were reviewed to better understand the role of hormonal factors and to determine whether reproductive events influence breast cancer risk differently according to age at diagnosis of breast cancer. Through a Medline/Pubmed search, 26 articles providing risk estimates by age at diagnosis of breast cancer or by menopausal status were analysed. A decrease of about 9% of breast cancer risk was found for each additional year at menarche when breast cancer was diagnosed early or before the menopause, and of about 4% when diagnosed late or after. Breast cancer risk increased with increasing age at FFTP by 5% per year for breast cancer diagnosed early or before the menopause and by 3% for cancers diagnosed late or after the menopause. Each full term pregnancy (or child) led to a 3% reduction in the risk of breast cancer diagnosed early or before the menopause, whereas the reduction attained 12% for the breast cancers diagnosed later. No change in the effect of these three factors with time (date of diagnosis of the breast cancer before 1980 or after) was observed. These results support the hypothesis of an age-specific effect of the three breast cancer risk factors considered herein, based on the time of initiation of the carcinogenic process. These observations underline the importance of the time of initiation of the carcinogenic process in determining the effect of promoters such as reproductive factors. This largely unexplored aspect of breast carcinogenesis might open the way for new prevention approaches.

Vitamin supplement use and breast cancer in a North Carolina population

OBJECTIVE

Laboratory data suggest that several different vitamins may inhibit the growth of mammary cancers, however epidemiologic data on the relationship between vitamin supplement use and breast cancer are inconsistent. We examined the association between self-reported vitamin supplement use and breast cancer among black women and white women.

DESIGN AND SETTING

The data came from a population-based, case-control study conducted in North Carolina between 1993 and 1996. Logistic regression models were used to calculate adjusted odds ratios (ORs) for breast cancer associated with the use of multivitamins or individual vitamin supplements.

SUBJECTS

Eligible cases were aged 20 to 74, and approximately 40% of the study population were black women. The analyses included 861 cases and 790 controls.

RESULTS

Among all women, there was little evidence for an association between any vitamin supplement and breast cancer. Modest inverse associations were observed among white women for use of multivitamins 95% confidence interval (CI): 0.59-1.12), vitamin C 95% CI: 0.54-1.14) and vitamin E 95% CI: 0.49-1.13). There was no evidence that vitamin supplements reduced the risk of breast cancer among black women.

CONCLUSIONS

This study provided very limited support for the hypothesis that vitamin supplements may reduce the risk of breast cancer. Although dietary factors are likely an important influence in breast cancer aetiology, reductions in risk are most likely to be achieved through dietary modification rather than through vitamin supplementation.

Genetic factors related to racial variation in plasma levels of insulin-like growth factor-1: implications for premenopausal breast cancer risk

The oral contraceptive pill is associated with a modest increase in the risk of early-onset breast cancer in the general population, but it is possible that the risk is higher in certain subgroups of women. The relative risk of breast cancer associated with oral contraceptive use has been reported to be higher for African-American women than for white women. African-American women also have a higher incidence of premenopausal breast cancer than white women. Circulating levels of insulin-like growth factor-1 (IGF-I) vary between ethnic groups and are positively associated with the risk of premenopausal breast cancer. In general, the plasma level of IGF-I is lower in women who take oral contraceptives than in women who do not. In an attempt to explain the observed ethnic difference in IGF-I levels with oral contraceptive use, we sought to identify polymorphic variants of genes that are associated with IGF-I levels and estrogen metabolism. We measured IGF-I and IGFBP-3 plasma levels in 503 nulligravid women between the ages of 17 and 35. All women filled out a questionnaire that included information about ethnic background and oral contraceptive use. Samples of DNA were used to genotype the women for known polymorphic variants in the IGF1, AIB1, and CYP3A4 genes. Black women had significantly higher mean IGF-I levels than white women (330 ng/ml versus 284 ng/ml; P = 0.001, adjusted for age and oral contraceptive use). IGF-I levels were significantly suppressed by oral contraceptives in white women (301 ng/ml versus 267 ng/ml; P = 0.0003), but not in black women. Among oral contraceptive users, the IGF-I level was positively associated with the absence of the IGF1 19-repeat allele (338 ng/ml versus 265 ng/ml; P = 0.00007), with the presence of the CYP3A4 variant allele (320 ng/ml versus 269 ng/ml; P = 0.01), and with the presence of the AIB1 26-repeat allele (291 ng/ml versus 271; P = 0.08). After adjusting for genotypes, ethnic group was no longer a significant predictor of the IGF-I level. IGF-I levels are higher among black than white women. Polymorphic variants in the CYP3A4, IGF1, and AIB1 genes are associated with increases in the plasma levels of IGF-I among oral contraceptive users and the variant alleles are much more common in black women than in white women. The high incidence of premenopausal breast cancer among black women may be mediated through genetic modifiers of circulating levels of IGF-I.

Breast carcinoma etiology: current knowledge and new insights into the effects of reproductive and hormonal risk factors in black and white populations

BACKGROUND

A crossover in breast carcinoma incidence at ages 45-49 years has been observed between black and white women, with blacks experiencing higher incidence at younger ages and lower incidence after age 50 years. Can this phenomenon be partially explained by the differences in the distributions of reproductive risk factors? This article focuses on the effects and distributions of age at first full term pregnancy (FFTP), parity, and oral contraceptive (OC) use in younger versus older and black and white populations. Effects of hormone replacement therapy (HRT) are also summarized.

METHODS

A literature review was conducted and information integrated on the effects and distributions of reproductive and hormonal risk factors in black and white populations, the crossover effect of parity, and the Pike model of "breast tissue age."

RESULTS

Overall, early age at FFTP and higher parity decreased risk for both races. Distributions of age at FFTP and parity varied widely between the two races. Based on the effects and distributions of age at FFTP and parity, the authors formulated the hypothesis that a crossover in incidence curves between the two races would be expected, rather than be considered an anomaly. Regarding OC use, generally a stronger increase in risk was observed for younger women than for older women. Regarding HRT, a recent meta-analysis observed an increased risk of 1.35 for 5 years of use or more.

CONCLUSIONS

To promote public health in diverse populations, and to provide further insight into breast carcinoma etiology, research needs to focus on multicultural differences and similarities in the relation of hormonal risk factors and breast carcinoma.

Health behavior change models and their socio-cultural relevance for breast cancer screening in African American women

Models of health behavior provide the conceptual bases for most of the breast cancer screening intervention studies. These models were not designed for and have not been adequately tested with African American women. The models discussed in this paper are: The Health Belief Model, the Theory of Reasoned Action/Theory of Planned Behavior, and the Transtheoretical Model. This paper will examine the socio-cultural relevance of these health behavior models, and discuss specific socio-cultural dimensions that are not accounted for by these paradigms. It is critical that researchers include socio-cultural dimensions, such as interconnectedness, health socialization, ecological factors and health care system factors into their intervention models with African American women. Comprehensive and socio-culturally based investigations are necessary to guide the scientific and policy challenge for reducing breast cancer mortality in African American women.

Ethnicity and variation in breast cancer incidence

A breast cancer case-control study in Atlanta and 5 counties of central New Jersey involving interviews with 960 white and 281 black cases younger than 54 years of age enabled assessment of reasons for the varying incidence rates among these 2 ethnic groups. Of interest was why rates of breast cancer are higher among older white women, a trend that is reversed among very young women (<40 years). Calculation of the prevalence of exposure to classic and speculative risk factors and associated relative risks enabled derivation of population attributable risks (PARs) for the various combinations of age and ethnic groups. A higher PAR was derived for older (40-54 years) white (62%) than black (54%) women, which appeared to account for the observed difference in incidence between the 2 ethnic groups. Most of the difference in PARs between older whites and blacks was accounted for by whites having fewer births, later ages at first birth and slightly higher risks associated with reproductive and menstrual factors. Consideration of only well-established breast cancer risk factors showed a PAR among older whites of 57%, an estimate comparable to those previously published. Slightly higher overall PARs were derived when analyses considered several speculative but modifiable risk factors, including years of use of oral contraceptives, body size and alcohol consumption. Many of the analyses among younger women (20-39 years) were limited by available numbers, but it appeared that very little disease occurrence in young black women was associated with the factors studied.

Oral contraceptive use and breast cancer risk among African-American women

Recent epidemiologic studies, most of them in predominantly White populations, have suggested that long duration of oral contraceptive (OC) use may increase the risk of breast cancer at young ages. We assessed the relationship of OC use to the risk of breast cancer in African-American women aged 25 to 59 years, using interview data from a multipurpose hospital-based case-control study. Five hundred and twenty-four cases hospitalized for invasive breast cancer were compared with 1,021 controls with nonmalignant conditions unrelated to OC use. Relative risks (RR) and 95 percent confidence intervals (CI) were estimated relative to a reference category of use for less than 12 months; potential confounders were controlled by multiple logistic regression analysis. Among women under age 45, three or more years of OC use was associated with an increased risk of breast cancer: the RR estimate was 2.8 (CI = 1.5-5.0) for three to four years of use, and declined to 1.5 (CI = 08.3.0) for 10 or more years of use. Recency and timing of use did not explain the observed association. Among women aged 45 to 59, OC use was associated with little or no increase in risk: the RR estimate for three or more years of use was 1.3 (CI = 0.7-2.4). The findings add to the evidence from studies of White women and a recent study of Black women which have suggested an increased risk of breast cancer at young ages for moderate or long duration use of OCs.