Risk factors for breast cancer in Turkish women: a hospital-based case-control study

The aim of this study was to investigate the association between risk factors and breast cancer in Turkish women. In a hospital-based case-control study in Istanbul, 405 patients with histologically confirmed breast cancer were compared with 1050 controls, who were admitted to different departments of the same hospital. Unadjusted odds ratios (ORs) and 95% confidence intervals (CIs) for each risk factor were obtained from logistic regression analyses. Risk factors for breast cancer were found to be early menarche age (OR 3.87, 95% CI 2.46-6.08), use of alcohol (OR 3.87, 95% CI 1.79-8.37), history of diabetes (OR 3.31, 95% CI 2.36-4.64) or hypertension (OR 3.44, 95% CI 2.07-5.71), oral contraceptive use (OR 1.98, 95% CI 1.38-2.85) and hormone replacement therapy (HRT) use (OR 1.94, 95% CI 1.15-3.29). The findings of the present study indicated that history of diabetes or hypertension, use of alcohol, oral contraceptive and HRT, never having breastfed and delayed age at first birth associated with changing of lifestyle led to an increased risk of breast cancer in Turkish women.     

Lactation and breast carcinoma risk in a South African population.

BACKGROUND: A number of epidemiologic studies have reported a reduced risk of breast carcinoma among women who have lactated but others have not. The current study presents data regarding lactation and breast carcinoma risk from a hospital-based case-control study of black and colored South African women. METHODS: Incident breast carcinoma cases treated between January 1994 and October 1997 (n = 446) at 2 major hospitals in Cape Town and hospital patients admitted for conditions unrelated to breast carcinoma (controls, n = 1471) were queried regarding the duration of breast-feeding each liveborn child and breast carcinoma risk factors. Multivariate logistic regression models were used to calculate odds ratios (ORs) for various categories of lactation compared with a reference category of never having breast-fed among women who had had at least one full term live birth. RESULTS: Approximately 83% of cases and 85% of controls had ever breast-fed (OR = 0.9; 95% confidence interval [95% CI], 0.7-1.3). Among all subjects, the ORs for those who lactated for <3 years were near or at unity. Beyond 3 years, ORs extending up to >/=7 years were less than unity, but the 95% CIs included 1.0 (OR for duration of >/=7 years = 0.7; 95% CI, 0.4-1.3). ORs did not vary by menopausal status. Breast carcinoma risk was not found to be related to the duration of breast-feeding the first child, the number of children breast-fed, or the patient's age at first lactation. CONCLUSIONS: The results of the current study suggest lactation has little or no protective effect on breast carcinoma risk.     

Breastfeeding reduces breast cancer risk: a case–control study in Tunisia

In this report, we examined the relationship between mother’s breastfeeding history and her risk of breast cancer, in a case–control study in Tunisia between 2006 and 2009. About 400 breast cancer cases and 400 controls were included. Cases and controls were interviewed using a standardized structured questionnaire to obtain information on breastfeeding and other risk factors. Mean duration of breastfeeding per child was significantly associated with a reduced risk of breast cancer for women who breastfed for >24 months per child. The OR was 0.46 (95% CI, 0.28–0.76) when compared those who breastfed for <6 months. The test for trend was significant (p = 0.01). A significantly reduced risk of breast cancer was found for those whose lifetime duration of breastfeeding was 73–108 months (OR = 0.65, 95% CI, 0.36–1.18) and for those who breastfed for ≥109 months (OR = 0.42, 95% CI, 0.20–0.84). Stratification by menopausal status showed a reduced risk of breast cancer associated with a longer duration of breastfeeding for both pre- and postmenopausal women. The risk reduction was more consistent for lifetime duration of breastfeeding, the test for trend being significant for both pre- (p = 0.03) and postmenopausal (p = 0.01) women. These results support an inverse association between breastfeeding and breast cancer risk.     

Exposure to breast milk in infancy and risk of breast cancer

Early life exposures, such as being breastfed in infancy, may influence the risk of breast cancer in adulthood. We evaluated the risk of breast cancer in relation to ever having been breastfed in infancy among 9,442 women who participated in a population-based, case–control study. Cases were identified through cancer registries in three states (Massachusetts, New Hampshire, and Wisconsin); controls were identified through statewide drivers’ license lists or medicare lists. Data on known and suspected risk factors were obtained through telephone interview. We used unconditional logistic regression to assess the relation of breast cancer with ever having been breastfed and with breastfeeding duration (available for only 19% of breastfed women) in premenopausal women (1,986 cases and 1,760 controls) and postmenopausal women (2,600 cases and 2,493 controls). We found no evidence that ever having been breastfed in infancy was associated with breast cancer risk in either premenopausal women (odds ratio [OR] = 0.96; 95% confidence interval [CI] = 0.83–1.10) or postmenopausal women (OR = 0.98; 95% CI = 0.87–1.10). The association did not differ according to breast cancer stage, mother’s history of breast cancer, or any other reproductive factor assessed. Likewise, we found no association between breastfeeding duration and risk of breast cancer. Our results did not support the hypothesis that exposure to breast milk in infancy influences the risk of adult breast cancer.     

Risk Factors for Breast Cancer in Iranian Women Aged Less than 40 Years

This case-control study was carried out in a university-affiliated teaching hospital, Tehran city, Iran. A total of312 newly diagnosed cases aged less than 40 years old participated and were matched for age and ethnicity with312 controls. The results showed that in women who never married (OR=2.42 95%CI=1.51-3.88) (P<0.001), hada family history of breast cancer (OR=7.07 95%CI=2.95-16.99) (P<0.001), a low age of menarche (OR=0.1 95%CI=0.04-0.23) (P<0.001)), lower parity (OR=13.3 95% CI=3.89-45.66) (P<0.001) and took oral contraceptive pills(OR= 2.83 95% CI=1.87-4.24) (P<0.000) were at increased risk. A direct association with age at first birth wasalso evident(P=0.041), with a significantly inverse association between duration of lactation and breast cancer risk(p=0.016). On multivariate logistic regression, parity, family history of breast cancer, use of oral contraceptivepills, and age at first birth remained significant. In women lower than 40 years of age, breast cancer risk wassignificantly higher in women with parity ≥4 compared with nulliparity but no association emerged with historyof breast-feeding. Other risk factors were similar to those described in breast cancer epidemiology at any age.     

Obstetric history and mammographic density: a population-based cross-sectional study in Spain (DDM-Spain)

High mammographic density (MD) is used as a phenotype risk marker for developing breast cancer. During pregnancy and lactation the breast attains full development, with a cellular-proliferation followed by a lobular-differentiation stage. This study investigates the influence of obstetric factors on MD among pre- and post-menopausal women. We enrolled 3,574 women aged 45-68 years who were participating in breast cancer screening programmes in seven screening centers. To measure MD, blind anonymous readings were taken by an experienced radiologist, using craniocaudal mammography and Boyd's semiquantitative scale. Demographic and reproductive data were directly surveyed by purpose-trained staff at the date of screening. The association between MD and obstetric variables was quantified by ordinal logistic regression, with screening centre introduced as a random effect term. We adjusted for age, number of children and body mass index, and stratified by menopausal status. Parity was inversely associated with density, the probability of having high MD decreased by 16% for each new birth (P value < 0.001). Among parous women, a positive association was detected with duration of lactation [>9 months: odds ratio (OR) = 1.33; 95% confidence interval (CI) = 1.02-1.72] and weight of first child (>3,500 g: OR = 1.32; 95% CI = 1.12-1.54). Age at first birth showed a different effect in pre- and post-menopausal women (P value for interaction = 0.030). No association was found among pre-menopausal women. However, in post-menopausal women the probability of having high MD increased in women who had their first child after the age of 30 (OR = 1.53; 95% CI = 1.17-2.00). A higher risk associated with birth of twins was also mainly observed in post-menopausal women (OR = 2.02; 95% CI = 1.18-3.46). Our study shows a greater prevalence of high MD in mothers of advanced age at first birth, those who had twins, those who have breastfed for longer periods, and mothers whose first child had an elevated birth weight. These results suggest the influence of hormones and growth factors over the proliferative activity of the mammary gland.     

Risk factors for breast cancer in Turkish women with early pregnancies and long-lasting lactation--a case-control study

A hospital-based case-control study was carried out among 504 women with breast cancer and 610 controls to analyse the risk factors for breast cancer in Turkey. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for each risk factor were obtained from logistic regression analysis. Risk factors for breast cancer were found to be long-term lactation (> or = 5 years versus never OR 0.31, 95% CI 0.12-0.79), young age at menarche (< 15 years versus > or = 15 OR 1.72, 95% CI 1.30-2.28), late age at first full-term pregnancy (> or = 30 versus < 20 OR 2.86, 95% CI 1.32-6.21), oral contraceptive use (ever versus never OR 1.51, 95% CI 1.10-2.08), positive family history (positive versus negative OR 2.81, 95% CI 1.35-5.82), and menstrual irregularity (yes versus no OR 1.61, 95% CI 1.05-2.49). The results of the present study will lead to a better understanding of the risk factors for breast cancer in a developing country.     

A case-control study of lactation and cancer of the breast.

We have examined the relation of lactation, by total duration, with breast cancer risk among pre- and post-menopausal women. In a hospital-based case-control study conducted in Athens (1989-91), involving 820 patients with confirmed breast cancer and 795 orthopaedic patient controls and 753 hospital visitor controls, logistic regression was used to analyse the data controlling for demographic, nutritional and reproductive factors, including parity and age at any birth. Among post-menopausal women, there was no association between breastfeeding and breast cancer risk, but among premenopausal women those who has breastfed for > or = 24 months had an odds ratio of 0.50 (95% confidence interval 0.23-1.41). A reduction of the odds ration was also evident among premenopausal women who had breastfed between 12 and 23 months (odds ratio 0.70; 95% confidence interval 0.34-1.60). In conjunction with several other recent reports these results support the hypothesis that breastfeeding of prolonged duration may reduce the risk of breast cancer among premenopausal women but not among post-menopausal women. The biology underlying this different effect remains unknown, and the practical implication of the finding is a marginal importance.     

Analysis of menstrual, reproductive, and life-style factors for breast cancer risk in Turkish women: a case-control study

The aim of this study was to investigate the association between menstrual, reproductive, and life-style factors and breast cancer in Turkish women. In a hospital-based case-control study in Ankara, 622 patients with histologically confirmed breast cancer were compared with 622 age-matched controls, admitted to the same hospital for acute and non-neoplastic diseases. Unconditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CI) related to risk factors. Overall, menopausal status and age at menopause were found to be significantly associated with breast cancer. Having a full-term pregnancy and early age at first birth were associated with decreased breast cancer risk (OR = 0.45, 95% CI = 0.30-0.66; OR = 0.34, 95% CI = 0.22-0.53, respectively). Postmenopausal women with lactation longer than 48 mo had reduced risk of breast cancer (OR = 0.36, 95% CI = 0.14-0.93). In conclusion, decreased parity, late age at first birth, early menopause, and shorter duration of lactation were the most important determinants of breast cancer risk in Turkish women.     

Glutathione S-transferase M1 and T1 genetic polymorphisms,alcohol consumption and breast cancer risk

Alcohol consumption has been inconsistently associated with breast cancer risk. Recent studies suggest that genetic polymorphisms of glutathione S-transferases (GSTs) may modify this relation. To determine if breast cancer risk is associated with GSTM1 and GSTT1 genetic polymorphisms, and to evaluate the effect modification between GST genotypes and alcohol consumption in the risk of breast cancer, we conducted a case-control study in the state of Connecticut in the period 1998 and 2001. Cases were histologically confirmed, incident breast cancer patients in New Haven County, CT. Controls were randomly selected from women histologically confirmed to be without breast cancer. The study results show that, while GSTM1 genotypes were not associated with breast cancer risk, GSTT1-null genotype was associated with a significant 90% increased risk for postmenopausal women (OR=1.9, 95% CI 1.2-3.0). Analysis by GST genotypes and alcohol consumption shows that GSTM1A ever-drinking women had a 2.5-fold (OR=2.5, 95% CI 1.1-5.5) increased risk of breast cancer compared to the GSTM1A never-drinkers, and the risk increases with duration and daily amount of alcohol consumption. Postmenopausal women with GSTT1-null genotype, who consumed a lifetime of >250 kg of spirit-equivalents, had an almost seven-fold increased risk (OR=6.8, 95% CI 1.4-33.9), and drinking commencing at younger ages appears to carry a higher risk. An OR of 8.2 (95% CI 1.2-57.4) was observed for those with GSTM1A, and GSTT1-null genotypes who had consumed a lifetime of >250 kg of spirit-equivalents. In conclusion, alcohol consumption may increase breast cancer risk among those who carry susceptible GST genotypes.     

Breast cancer risk in symptomatic women spontaneously undergoing clinical breast examination

Breast cancer (BC) is the most common cancer among women. However, few studies consider the possible relationship between the main breast complaints referred to by non-screened patients and cancer onset. The objective of this study was to evaluate the relationship between the principal breast complaints (breast pain, breast lump and nipple discharge) and the risk of BC. A group of 347 symptomatic women (median age 59 years, range 35-83) with confirmed BC (cases) was age-matched with a population-based group of 351 symptomatic women (controls) who were followed-up for at least three years (median 78 months, range 36-146) to exclude the presence of a missed BC. Breast pain was the most common (p < 0.05) complaint in younger patients (50 years or less = 39.0%, 51-60 years = 51.2%), while breast lump was most common in patients aged > 60 years (65.4%). Since the odds ratio (OR) ranged from 0.80 to 1.20 at a 95% confidence interval (CI) of 0.54-1.80, there was no overall significant association between breast complaints and risk of BC. There was some evidence of increased risk among patients with breast lump (OR = 1.20, 95% CI 0.80-1.80), and no risk in those with breast pain (OR = 0.86, 95% CI 0.54-1.36) and nipple discharge (OR = 0.8, 95% CI 0.37-1.74). In conclusion, a relationship between breast complaints and the onset of BC does not seem to exist.     

Oral contraceptive use and mammographic patterns.

High-risk mammographic patterns represent an increased risk of contracting breast cancer and may be used as a surrogate endpoint for the disease. We examined the relationship between oral contraceptive (OC) use and mammographic patterns among 3218 Norwegian women, aged 40-56 years. Information on ever OC use, duration, and age of first OC use and other epidemiological data were obtained through questionnaires. The mammograms were categorized into five groups. Patterns I-III were combined into a low-risk group and patterns IV and V into a high-risk group. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using logistic regression and adjusted for age, menopausal status, parity, age at first birth, and body mass index. Women who reported ever having used OCs were 20% more likely (OR 1.27, 95% CI 1.0-1.6) to have high-risk mammographic patterns compared with those reporting never having used OCs. There was no dose response between different measures of OC use and high-risk patterns. Among nulliparous women, ever OC users were four times more likely (OR 4.65, 95% CI 2.1-10.3) to have high-risk patterns compared with never users. Our findings suggest that, especially among nulliparous women, ever OC use may exert its effect on breast cancer risk through changes in breast tissue, which can be observed on a mammogram.     

Effect of lifetime lactation on breast cancer risk: a Korean women's cohort study

The objective of our study was to examine the effect of lifetime lactation on breast cancer risk among premenopausal women. The data were from a prospective cohort study with a follow-up period of 6 years in Korea (1995-2000). The cohort was composed of 110,604 premenopausal parous Korean women, aged 20 years and older, who received health insurance from the Korea Medical Insurance Corporation and who had medical evaluations in 1992 and 1994. Multivariate Cox proportional hazard models were tested, controlling for age, age at menarche, number of children, age at first pregnancy, oral contraceptive use, smoking, exercise and obesity. At baseline, 57,440 (51.9%) reported breastfeeding and 4,584 (4.1%) reported breastfeeding more than 24 months. From 1995-2000, 360 incident cases of breast cancer (61.8/100,000 person-years) occurred. Compared to parous women who had no history of lactation, a period of lactation of 13-24 months decreased the risk of breast cancer (RR, 0.7; 95% CI, 0.5-1.1), and this risk was decreased even further for those who breastfed for more than 24 months (RR, 0.6; 95% CI, 0.3-1.0). There was a clear trend of decreasing breast cancer risk with the duration of lactation (p for trend <0.001). In conclusion, our study of a large Korean cohort provides additional empirical evidence to current theoretical conjecture that lactation decreases the risk of breast cancer among premenopausal women.     

Lifetime exercise activity and breast cancer risk among post-menopausal women.

Lifetime exercise activity has been linked to breast cancer risk among young women. However, no study has specifically evaluated whether lifetime exercise activity is related to the breast cancer risk of post-menopausal women. We conducted a population-based case-control study of post-menopausal white women (1123 newly diagnosed cases and 904 healthy controls) aged 55-64 who lived in Los Angeles County, California, USA to evaluate this relationship. Although neither exercise activity from menarche to age 40 years, nor exercise after age 40 separately predicted breast cancer risk, risk was lower among women who had exercised each week for at least 17.6 MET-hours (metabolic equivalent of energy expenditure multiplied by hours of activity) since menarche than among inactive women (odds ratio (OR) = 0.55; 95% confidence interval (CI) 0.37-0.83). Exercise activity was not protective for women who gained considerable (> 17%) weight during adulthood. However, among women with more stable weight, breast cancer risk was substantially reduced for those who consistently exercised at high levels throughout their lifetime (OR = 0.42; 95% CI 0.24-0.75), those who exercised more than 4 h per week for at least 12 years (OR = 0.59; 95% CI 0.40-0.88), and those who exercised vigorously (24.5 MET-hours per week) during the most recent 10 years (OR = 0.52; 95% CI 0.32-0.85). Strenuous exercise appears to reduce breast cancer risk among post-menopausal women who do not gain sizable amounts of weight during adulthood.     

Genetic polymorphisms in the apoptosis-associated genes FAS and FASL and breast cancer risk

FAS and FAS ligand (FASL) play key roles in apoptotic signaling and down-regulation of this pathway may facilitate tumorigenesis. Alterations in apoptosis genes may affect cancer risk by influencing individual susceptibility to environmental carcinogens. Using a population-based breast cancer case-control study on Long Island, New York, we examined whether polymorphisms in FAS and FASL modified the association between breast cancer risk and a marker of environmental exposures, polycyclic aromatic hydrocarbon (PAH)-DNA adducts. We examined polymorphisms in FAS (5' UTR -1377G/A and 5' UTR -670G/A) and FASL (5' UTR -844C/T) in 1053 breast cancer cases and 1102 population-based controls. There was no significant association between these genetic polymorphisms and breast cancer risk. The presence of at least one variant allele (GA or AA) in FAS1377 was associated with a 36% increase in breast cancer risk among those with detectable PAH-DNA adduct levels [odds ratio (OR) = 1.36, 95% confidence interval (CI) = 1.01-1.83]. In addition, lactation history significantly modified the association between FAS1377 and FAS670 genetic variants and breast cancer risk (OR = 1.46, 95% CI = 1.04-2.06 and OR = 1.71, 95% CI = 1.13-1.58, respectively, in those who ever lactated compared with those who did not with the wild-type alleles). Overall, this study suggests that the risk of breast cancer may be elevated among women with polymorphisms in the FAS gene and detectable PAH-DNA adducts.     

The CYP1A2 genotype modifies the association between coffee consumption and breast cancer risk among BRCA1 mutation carriers.

We have recently reported that, among BRCA1 mutation carriers, the consumption of caffeinated coffee was associated with a significant reduction in breast cancer risk. Because the metabolism of caffeine is primarily by CYP1A2, we examined whether or not the CYP1A2 genotype modifies the association between a history of coffee consumption and the risk of breast cancer. A common A to C polymorphism in the CYP1A2 gene is associated with decreased enzyme inducibility and impaired caffeine metabolism. Information regarding coffee consumption habits and the CYP1A2 genotype was available for 411 BRCA1 mutation carriers (170 cases and 241 controls). We estimated the odds ratios (ORs) and 95% confidence intervals (95% CIs) for breast cancer associated with the CYP1A2 genotype and a history of coffee consumption before age 35, adjusting for potential confounders. The CYP1A2 genotype did not affect breast cancer risk. Among women with at least one variant C allele (AC or CC), those who consumed coffee had a 64% reduction in breast cancer risk, compared with women who never consumed coffee (OR, 0.36; 95% CI, 0.18-0.73). A significant protective effect of coffee consumption was not observed among women with the CYP1A2 AA genotype (OR, 0.93; 95% CI, 0.49-1.77). Similar results were obtained when the analysis was restricted to caffeinated coffee. This study suggests that caffeine protects against breast cancer in women with a BRCA1 mutation and illustrates the importance of integrating individual genetic variability when assessing diet-disease associations.     

Prolonged lactation reduces ovarian cancer risk in Chinese women.

To investigate the effect of lactation on the risk of ovarian cancer for Chinese women, a case-control study was conducted in Hangzhou, capital of Zhejiang province, China. Cases were 275 patients with histologically confirmed epithelial ovarian cancer. Controls were 623 women without neoplasm. All participants were parous women who had given at least one live birth and had been residents of Zhejiang province for at least 10 years. Information was collected using a validated and reliable questionnaire on total months of lactation, number of children breastfed, and average duration of lactation per child. Multivariate logistic regression models were used to assess the association between ovarian cancer risk and lactation variables, accounting for age, locality, full-term pregnancy, oral contraceptive use and family history of the cancer. The adjusted odds ratios were 0.51 (95% confidence interval (CI) 0.3-0.9) and 0.44 (95% CI 0.2-0.9) respectively for women with over 12 months of lactation and at least three children breastfed, compared with those with 4 months or less lactation and one child breastfed. The corresponding dose-response relationships were also significant (P<0.05). Therefore, prolonged lactation could reduce the risk of ovarian cancer for Chinese women.     

Breastfeeding and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers

INTRODUCTION: Breastfeeding has been inversely related to breast cancer risk in the general population. Clarifying the role of breastfeeding among women with a BRCA1 or BRCA2 mutation may be helpful for risk assessment and for recommendations regarding prevention. We present an updated analysis of breastfeeding and risk of breast cancer using a large matched sample of BRCA mutation carriers. METHODS: We conducted a case-control study of 1,665 pairs of women with a deleterious mutation in either BRCA1 (n = 1,243 pairs) or BRCA2 (n = 422 pairs). Breast cancer cases and unaffected controls were matched on year of birth, mutation status, country of residence and parity. Information about reproductive factors, including breastfeeding for each live birth, was collected from a routinely administered questionnaire. Conditional logistic regression was used to estimate the association between ever having breastfed, as well as total duration of breastfeeding, and the risk of breast cancer. RESULTS: Among BRCA1 mutation carriers, breastfeeding for at least one year was associated with a 32% reduction in risk (OR = 0.68; 95% CI 0.52 to 0.91; P = 0.008); breastfeeding for two or more years conferred a greater reduction in risk (OR = 0.51; 95% CI 0.35 to 0.74). Among BRCA2 mutation carriers, there was no significant association between breastfeeding for at least one year and breast cancer risk (OR = 0.83; 95% CI 0.53 to 1.31; P = 0.43). CONCLUSIONS: These data extend our previous findings that breastfeeding protects against BRCA1-, but not BRCA2-associated breast cancer. BRCA mutation carriers should be advised of the benefit of breastfeeding in terms of reducing breast cancer risk.     

Differences in estrogen receptor subtype according to family history of breast cancer among Hispanic, but not non-Hispanic White women

BACKGROUND: Pathologic differences have been reported among breast tumors when comparing ethnic populations. Limited research has been done to evaluate the ethnic-specific relationships between breast cancer risk factors and the pathologic features of breast tumors. METHODS: Given that genetic variation may contribute to ethnic-related etiologic differences in breast cancer, we hypothesized that tumor characteristics differ according to family history of breast cancer among Hispanic and non-Hispanic White (NHW) women. Logistic regression models were used to compute odds ratios (OR) and 95% confidence intervals (95% CI) to assess this relationship in the population-based, case-control 4-Corners Breast Cancer Study (1,537 cases and 2,452 controls). RESULTS: Among Hispanic women, having a family history was associated with a 2.7-fold increased risk of estrogen receptor (ER) negative (95% CI, 1.59-4.44), but not ER positive tumors (OR, 1.04; 95% CI, 0.71-1.54) when compared with women without breast cancer. In contrast, there was an increased risk for ER positive (OR, 1.89; 95% CI, 1.50-2.38) and a marginally significant increased risk for ER negative tumors (OR, 1.41; 95% CI, 0.92-2.17) among NHW women. When comparing tumor characteristics among invasive cases, those with a family history also had a significantly higher proportion of ER negative tumors among Hispanics (39.2% versus 25.8%; P=0.02), but not among NHWs (16.3% versus 21.1%; P=0.13). CONCLUSIONS: These results may reflect ethnic-specific predisposing genetic factors that promote the development of specific breast tumor subtypes, and emphasize the importance of evaluating the relationship between breast cancer risk factors and breast tumor subtypes among different ethnic populations.     

Risk factors for hormone receptor-defined breast cancer in postmenopausal women.

The effect of classic breast cancer risk factors on hormone receptor-defined breast cancer is not fully clarified. We explored these associations in a Swedish population-based study. Postmenopausal women ages 50 to 74 years, diagnosed with invasive breast cancer during 1993 to 1995, were compared with 3,065 age frequency-matched controls. We identified 332 estrogen receptor (ER-) and progesterone receptor (PR-) negative, 286 ER+PR-, 71 ER-PR+, 1,165 ER+PR+, and 789 tumors with unknown receptor status. Unconditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI). Women ages >or=30 years, compared with those ages 20 to 24 years at first birth, were at an increased risk of ER+PR+ tumors (OR, 1.5; 95% CI, 1.2-1.8) but not ER-PR- tumors (OR, 1.1; 95% CI, 0.8-1.6). Women who gained >or=30 kg in weight during adulthood had an approximately 3-fold increased relative risk of ER+PR+ tumors (OR, 2.7; 95% CI, 1.9-3.8), but no risk increase of ER-PR- tumors (OR, 1.0; 95% CI, 0.5-2.1), compared with women who gained <10 kg. Compared with never users, women who used menopausal estrogen-progestin therapy for at least 5 years were at increased risk of ER+PR+ tumors (OR, 3.0; 95% CI, 2.1-4.1) but not ER-PR- tumors (OR, 1.3; 95% CI, 0.7-2.5). In conclusion, other risk factors were similarly related to breast cancer regardless of receptor status, but high age at first birth, substantial weight gain in adult age, and use of menopausal estrogen-progestin therapy were more strongly related to receptor-positive breast cancer than receptor-negative breast cancer.