Coffee and black tea consumption and breast cancer mortality in a cohort of Swedish women

Background:Coffee and black tea contain a mixture of compounds that have the potential to influence breast cancer risk and survival. However, epidemiologic data on the relation between coffee and black tea consumption and breast cancer survival are sparse.Methods:We investigated the association between coffee and black tea consumption and survival among 3243 women with invasive breast cancer in the Swedish Mammography Cohort. Intake was estimated using a food frequency questionnaire. Cox proportional hazard models were used to calculate hazard ratios (HRs) and 95% confidence intervals (95% CIs).Results:From 1987 to 2010 there were 394 breast cancer-specific deaths and 973 total deaths. Coffee and black tea were not associated with breast cancer-specific or overall mortality. Women consuming 4+ cups of coffee per day had a covariate and clinical characteristics-adjusted HR (95% CI) of death from breast cancer of 1.14 (0.71-1.83; p(trend)=0.81) compared with those consuming <1 cup per day. Women consuming 2+ cups of black tea per day had a covariate and clinical characteristics-adjusted HR (95% CI) of death from breast cancer of 1.02 (0.67-1.55; p(trend)=0.94) compared with non-tea drinkers. Caffeine was also not associated with breast cancer-specific (HR for top to bottom quartile=1.06; 95% CI=0.79-1.44; p(trend)=0.71) or overall mortality.Conclusion:Our findings suggest that coffee, black tea, and caffeine consumption before breast cancer diagnosis do not influence breast cancer-specific and overall survival.     

Glycemic load,glycemic index and breast cancer risk in a prospective cohort of Swedish women

High‐glycemic load diets have been hypothesized to increase the risk of breast cancer but epidemiologic studies have yielded inconsistent findings. We examined the associations of carbohydrate intake, glycemic index and glycemic load with risk of overall and hormone receptor‐defined breast cancer in the Swedish Mammography Cohort, a population‐based cohort of 61,433 women who completed a food frequency questionnaire at enrollment in 1987–1990. During a mean follow‐up of 17.4 years, we ascertained 2,952 incident cases of invasive breast cancer. Glycemic load but not carbohydrate intake or glycemic index was weakly positively associated with overall breast cancer risk (p for trend = 0.05). In analyses stratified by estrogen receptor (ER) and progesterone receptor (PR) status of the breast tumors, we observed statistically significant positive associations of carbohydrate intake, glycemic index and glycemic load with risk of ER+/PR? breast cancer; the multivariate relative risks comparing extreme quintiles were 1.34 [95% confidence interval (CI) = 0.93–1.94; p for trend = 0.04] for carbohydrate intake, 1.44 (95% CI = 1.06–1.97; p for trend = 0.01) for glycemic index and 1.81 (95% CI = 1.29–2.53; p for trend = 0.0008) for glycemic load. No associations were observed for ER+/PR+ or ER?/PR? breast tumors. These findings suggest that a high carbohydrate intake and diets with high glycemic index and glycemic load may increase the risk of developing ER+/PR? breast cancer. © 2009 UICC     

Alcohol intake and mortality among women with invasive breast cancer

Background:

Alcohol intake has consistently been associated with increased breast cancer incidence in epidemiological studies. However, the relation between alcohol and survival after breast cancer diagnosis is less clear.

Methods:

We investigated whether alcohol intake was associated with survival among 3146 women diagnosed with invasive breast cancer in the Swedish Mammography Cohort. Alcohol consumption was estimated using a food frequency questionnaire. Cox proportional hazard models were used to calculate hazard ratios (HRs) and 95% confidence intervals (95% CIs).

Results:

From 1987 to 2008 there were 385 breast cancer-specific deaths and 860 total deaths. No significant association was observed between alcohol intake and breast cancer-specific survival. Women who consumed 10 g per day (corresponding to approximately 0.75 to 1 drinks) or more of alcohol had an adjusted HR (95% CI) of breast cancer-specific death of 1.36 (0.82–2.26;p_trend=0.47) compared with non-drinkers. A significant inverse association was observed between alcohol and non-breast cancer deaths. Those who consumed 3.4–9.9 g per day of alcohol had a 33% lower risk of death compared with non-drinkers (95% CI 0.50–0.90;p_trend=0.04).

Conclusion:

Our findings suggest that alcohol intake up to approximately one small drink per day does not negatively impact breast cancer-specific survival and a half drink per day is associated with a decreased risk of mortality from other causes.     

A nationwide epidemiologic study of breast cancer incidence following breast reduction surgery in a large cohort of Swedish women

Summary While it has been demonstrated that prophylactic mastectomy reduces breast cancer incidence among women at high risk, many women often consider this disfiguring surgery unacceptable. One alternative approach may be breast reduction surgery. In order to evaluate the long-term incidence of breast cancer following surgical removal of breast tissue, we have extended by 9 years the follow-up period of our earlier retrospective cohort study of Swedish women electing cosmetic breast reduction surgery (n=30,444) between 1965 and 1993, yielding an average of nearly 16 years of follow-up. Cancer incidence through 2002 was ascertained via the Swedish Cancer Registry. Standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) were calculated comparing women who underwent breast reduction surgery with women in the general Swedish population. Breast cancer was observed in 443 women versus 624 expected for a statistically significant reduced SIR of 0.71 (95% CI=0.65–0.78). Analyses by age at surgery, time since surgery or calendar year of surgery revealed similar reductions in risk. Our study of over 30,000 women with long-term follow-up offers further evidence that women undergoing breast reduction surgery have reduced breast cancer risk. As the evidence from large-scale cohort studies accumulates, direct testing of this reduction in risk through clinical trials should be considered.     

Folate intake and breast cancer mortality in a cohort of Swedish women

Folate may influence breast cancer development and progression through its role in one-carbon metabolism. However, epidemiologic data on the relation between folate and breast cancer survival are limited. We investigated whether dietary folate intake was associated with survival in 3,116 women diagnosed with breast cancer in the population-based Swedish Mammography Cohort. Participants completed a 67-item food frequency questionnaire in 1987. Cox proportional hazard models were used to calculate hazard ratios (HRs) and 95% confidence intervals (95% CIs) for death from breast cancer and death from any cause. During 25,716 person-years of follow-up from 1987 to 2008, there were 852 deaths with 381 breast cancer deaths. Dietary folate intake was inversely associated with breast cancer and overall mortality. Women in the highest quartile of folate intake had a multivariable HR (95% CI) of death from breast cancer of 0.78 (0.58–1.03) compared to those in the lowest quartile (P _trend = 0.03). The corresponding HR (95% CI) for death from any cause was 0.79 (0.66–0.96; P _trend = 0.004). The protective association between dietary folate intake and breast cancer death was strongest among those with ER-negative tumors (HR = 0.42; 95% = CI 0.22–0.79; P _trend = 0.01) comparing the highest to lowest quartile. Our findings suggest that folate intake before breast cancer diagnosis may improve breast cancer and overall survival. While these findings need to be confirmed in future studies, they do offer assurance that dietary folate intake at the levels observed in our population does not unfavorably affect survival after breast cancer.     

Selenium intake and breast cancer mortality in a cohort of Swedish women

Selenium is an important cofactor in the production of antioxidant enzymes that may influence cancer progression. Selenium intake and cancer survival has not been extensively studied; however, selenium supplementation has been demonstrated to reduce cancer mortality in nutritional intervention trials. We investigated whether dietary selenium intake was associated with survival among 3,146 women diagnosed with invasive breast cancer in the population-based Swedish Mammography Cohort. Selenium intake before breast cancer diagnosis was estimated using a food frequency questionnaire completed in 1987. Cox proportional hazard models were used to calculate hazard ratios (HRs) and 95 % confidence intervals (95 % CIs) for death from breast cancer, non-breast cancer death, and death from any cause. During 28,172 person-years of follow-up from 1987 to 2009, there were 416 breast cancer-specific deaths and 964 total deaths. Dietary selenium intake was inversely associated with breast cancer-specific mortality and overall mortality. Women in the highest quartile of selenium intake had a multivariable HR (95 % CI) of death from breast cancer of 0.69 (0.52-0.92) compared with those in the lowest quartile (P (trend) = 0.009). The inverse association between dietary selenium intake and breast cancer death appeared strongest among women who had ever smoked (HR = 0.34; 95 % CI 0.14-0.83; P (trend) = 0.01) comparing the highest to lowest quartile. Our findings suggest that selenium intake before breast cancer diagnosis may improve breast cancer-specific survival and overall survival. However, these results may be limited to populations with low intakes of selenium.     

Tea consumption and breast cancer risk in a cohort of women with family history of breast cancer

Laboratory studies have observed chemopreventive effects of black and green tea on breast cancer development, but few epidemiologic studies have identified such effects. We investigated the association between tea consumption and breast cancer risk using data from 45,744 U.S. and Puerto Rican women participating in the Sister Study. Frequency and serving size of black and green tea consumption were measured at cohort enrollment. Breast cancer diagnoses were reported during follow-up and confirmed by medical record review. Multivariable Cox proportional hazards regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI). We further investigated potential variation according to estrogen receptor (ER) status, menopausal status and body mass index (BMI). Overall, 81.6 and 56.0% of women drank black or green tea, respectively. A total of 2,809 breast cancer cases were identified in the cohort. The multivariable model suggested an inverse association between black (≥5 vs. 0 cups/week: HR = 0.88, 95% CI 0.78, 1.00, p-trend = 0.08) and green tea (≥5 vs. 0 cups/week: HR = 0.82, 95% CI 0.70, 0.95, p-trend < 0.01) consumption and breast cancer risk. We did not observe differences by ER characteristics, menopausal status or BMI. In conclusion, our study suggests drinking at least five cups of green or black tea per week may be associated with decreased breast cancer risk.     

Long‐term dietary acrylamide intake and risk of endometrial cancer in a prospective cohort of Swedish women

Acrylamide has been found in foods heated at high temperatures and there is evidence of carcinogenicity of acrylamide in experimental animals. However, the potential health risks of dietary acrylamide intake in humans remain uncertain. We examined the association between dietary acrylamide intake and the incidence of endometrial cancer among 61,226 participants of the Swedish Mammography Cohort who were cancer‐free at enrollment in 1987–1990 and completed a food frequency questionnaire at baseline and again in 1997. Cox proportional hazards models were used to estimate rate ratios with 95% confidence intervals, adjusted for endometrial cancer risk factors. During a mean follow‐up of 17.7 years, a total of 687 incident cases of endometrial adenocarcinoma were diagnosed in the cohort. We found no association between long‐term acrylamide intake and risk of endometrial cancer. The multivariate rate ratio of endometrial cancer for women in the highest quartile of acrylamide intake (mean, 33.8 μg/day) compared to those in the lowest quartile (mean, 15.9 μg/day) was 0.96 (95% CI, 0.76–1.21). The association did not vary materially by smoking status. In conclusion, these findings do not support the hypothesis that dietary acrylamide intake is positively associated with risk of endometrial cancer, at least not within the ranges of acrylamide consumed in this population. © 2008 Wiley‐Liss, Inc.     

Antioxidant supplement use after breast cancer diagnosis and mortality in the Life After Cancer Epidemiology (LACE) cohort

BACKGROUND:

There is concern that antioxidant supplement use during chemotherapy and radiation therapy may decrease treatment effects, yet the effects of such supplements on recurrence and survival are largely unknown.

METHODS:

The authors prospectively examined the associations between antioxidant use after breast cancer (BC) diagnosis and BC outcomes in 2264 women in the Life After Cancer Epidemiology (LACE) cohort. The cohort included women who were diagnosed with early stage, primary BC from 1997 to 2000 who enrolled, on average, 2 years postdiagnosis. Baseline data were collected on antioxidant supplement use since diagnosis and other factors. BC recurrence and mortality were ascertained, and hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using delayed entry Cox proportional hazards models. All tests of statistical significance were 2‐sided.

RESULTS:

Antioxidant supplement use after diagnosis was reported by 81% of women. Among antioxidant users, frequent use of vitamin C and vitamin E was associated with a decreased risk of BC recurrence (vitamin C: HR, 0.73; 95% CI, 0.55‐0.97; vitamin E: HR, 0.71; 95% CI, 0.54‐0.94); and vitamin E use was associated with a decreased risk of all‐cause mortality (HR, 0.76; 95% CI, 0.58‐1.00). Conversely, frequent use of combination carotenoids was associated with increased risk of death from BC (HR, 2.07; 95% CI, 1.21‐3.56) and all‐cause mortality (HR, 1.75; 95% CI, 1.13‐2.71).

CONCLUSIONS:

Frequent use of vitamin C and vitamin E in the period after BC diagnosis was associated with a decreased likelihood of recurrence, whereas frequent use of combination carotenoids was associated with increased mortality. The effects of antioxidant supplement use after diagnosis likely differ by type of antioxidant. Cancer 2012. © 2011 American Cancer Society.     

Vitamin D intake,blood 25(OH)D levels,and breast cancer risk or mortality: a meta-analysis

Background:

Experimental studies suggest potential anti-carcinogenic properties of vitamin D against breast cancer risk, but the epidemiological evidence to date is inconsistent.

Methods:

We searched MEDLINE and EMBASE databases along with a hand search for eligible studies to examine the association between vitamin D status (based on diet and blood 25-hydroxyvitamin D (25(OH)D)) and breast cancer risk or mortality in a meta-analysis. A random-effect model was used to calculate a pooled adjusted relative risk (RR).

Results:

A total of 30 prospective studies (nested case-control or cohort) were included for breast cancer incidence (n=24 studies; 31 867 cases) or mortality (n=6 studies; 870 deaths) among 6092 breast cancer patients. The pooled RRs of breast cancer incidence for the highest vs the lowest vitamin D intake and blood 25(OH)D levels were 0.95 (95% CI: 0.88–1.01) and 0.92 (95% CI: 0.83–1.02), respectively. Among breast cancer patients, high blood 25(OH)D levels were significantly associated with lower breast cancer mortality (pooled RR=0.58, 95% CI: 0.40–0.85) and overall mortality (pooled RR=0.61, 95% CI: 0.48–0.79). There was no evidence of heterogeneity and publication bias.

Conclusions:

Our findings suggest that high vitamin D status is weakly associated with low breast cancer risk but strongly associated with better breast cancer survival.     

Coffee consumption and stomach cancer risk in a cohort of Swedish women

Few prospective studies have examined the relationship between coffee consumption and risk of stomach cancer, and the findings have been inconsistent. We prospectively investigated the association of long-term coffee consumption with risk of stomach cancer in a population-based cohort study of 61,433 Swedish women. Information on coffee consumption was collected with a food-frequency questionnaire at baseline (1987-1990) and updated in 1997. During a mean follow-up of 15.7 years from 1987 through June 2005, 160 incident cases of stomach cancer were diagnosed. Coffee consumption was positively associated with the risk of stomach cancer. Compared to women who consumed 1 or fewer cups of coffee per day, the multivariate hazard ratios were 1.49 (95% = 0.97-2.27) for women who drank 2-3 cups per day and 1.86 (95% CI = 1.07-3.25) for those who drank 4 or more cups per day (p for trend = 0.01). An increase of 1 cup of coffee per day was associated with a statistically significant 22% increased risk of stomach cancer (hazard ratio = 1.22; 95% CI = 1.05-1.42). These prospective data suggest that coffee consumption may increase the risk of stomach cancer in a dose-response manner. This finding needs to be confirmed in other prospective studies.     

Dietary acrylamide intake and risk of breast cancer in the UK women's cohort

Background:

No studies to date have demonstrated a clear association with breast cancer risk and dietary exposure to acrylamide.

Methods:

A 217-item food frequency questionnaire was used to estimate dietary acrylamide intake in 33 731 women aged 35–69 years from the UK Women''s Cohort Study followed up for a median of 11 years.

Results:

In all, 1084 incident breast cancers occurred during follow-up. There was no evidence of an overall association between acrylamide intake and breast cancer (hazard ratio=1.08 per 10 μg day⁻¹, 95% CI: 0.98–1.18, P_trend=0.1). There was a suggestion of a possible weak positive association between dietary acrylamide intake and premenopausal breast cancer after adjustment for potential confounders (hazard ratio=1.2, 95% CI: 1.0–1.3, P_trend=0.008). There was no suggestion of any association for postmenopausal breast cancer (hazard ratio=1.0, 95% CI: 0.9–1.1, P_trend=0.99).

Conclusions:

There is no evidence of an association between dietary acrylamide intake and breast cancer. A weak association may exist with premenopausal breast cancer, but requires further investigation.     

Vitamin D supplements and cancer incidence and mortality: a meta-analysis

Background:

Observational studies suggest that effects of vitamin D may be stronger for cancer mortality than for incidence. Yet, existing randomised controlled trials (RCTs) of vitamin D supplementation have limited power to examine the relationships as their primary end points are not cancer incidence or mortality.

Methods:

Meta-analyses of RCTs of vitamin D supplementation and total cancer incidence and mortality were conducted.

Results:

Over 2–7 years of duration, vitamin D supplementations had little effect on total cancer incidence (400–1100 IU per day, summary relative risk (RR)=1.00, 95% confidence interval (CI)=0.94–1.06, I²=0% four RCTs with combined 4333 cases), but significantly reduced total cancer mortality (400–833 IU per day, summary RR=0.88, 95% CI=0.78–0.98, I²=0%, three RCTs with combined 1190 deaths).

Conclusions:

Over 2–7 years of duration, the benefit of vitamin D supplementation may be limited to cancer mortality.     

Intake of vitamins A, C, and E from diet and supplements and breast cancer in postmenopausal women

Objective: The influence of the vitamins A, C, and E on breast cancer development has not been clarified. An effect of a vitamin per se implicates similar patterns for the effects of the vitamin from dietary and supplemental sources. We examined how the breast cancer incidence rate among postmenopausal women was related to intake of vitamins A, C, and E from diet and supplements. Methods: Data was sampled as case–control nested within the Danish Diet, Cancer and Health cohort. Data on vitamin intakes were collected at entry into the cohort by means of self-administered questionnaires. Women eligible for the nested case–control study were postmenopausal at entry into the cohort. The analyses were based on 418 cases of incident breast cancer and 394 controls (including two cases). Results: Breast cancer was not significantly related to the intakes of vitamin A or E, whereas a monotonic dose–response relation was seen for the intake of vitamin C. The estimated rate ratio per 100 mg vitamin C was: 2.06 (95% CI: 1.45–2.91) for dietary intake and 1.06 (95% CI: 1.01–1.13) for supplemental intake. Conclusions: We found no evidence of an association between breast cancer and intake of vitamin A or E for postmenopausal women. For vitamin C we found an increase in breast cancer rate with increasing intake.     

Organised mammography screening reduces breast cancer mortality: a cohort study from Finland

We evaluated the effectiveness and the efficacy of population-based mammography programme in Finland, and explored associations between the screening performance and the screening efficacy. The main outcome, incidence-based mortality from breast cancer, was estimated by invitation, participation, age at death, and screening centres categorised by recall rates. The study was based on an individual followup of screening invitees and participants from 1992 to 2003. The coverage of screening invitations was 95% among 50-59 years old women, and 20-40% among women aged 60-69 years. We compared observed deaths from breast cancer to expected breast cancer deaths without screening in ages 50-69 at death. The observed deaths were obtained from a cohort of individual invitees (n = 361,848). The expected deaths were defined by modelling breast cancer mortality from 1974 to 1985 and 1992 to 2003 at population level. The population data were derived from the same municipalities (n = 260) that were incorporated into the cohort. The breast cancer mortality among the invited women was reduced by 22% (relative risk 0.78, 95% confidence interval 0.70-0.87). After adjusting for the self-selection, the efficacy among the participants was 28% (0.72,0.56-0.88). No clear association between the recall rates and the screening efficacy was observed. The organised mammography screening in Finland is effective. The relationship between the estimates of process and outcome of mammography is not yet straightforward: effectiveness and efficacy remain the best estimates for evaluating the success of mammography screening.     

淮安市女性乳腺癌发病和死亡分析

目的分析淮安市2009-2011年女性乳腺癌发病与死亡的流行特征,为乳腺癌的防治工作提供依据。方法利用淮安市恶性肿瘤登记报告工作收集淮安市2009-2011年女性乳腺癌的发病和死亡数据,分年龄、地区(城市和农村)分析淮安市乳腺癌流行病学特征。结果淮安地区2009-2011年乳腺癌发病共1 225例,粗发病率16.01/10万,城市20.22/10万,农村11.77/10万;标化发病率为13.19/10万,城市16.33/10万,农村10.03/10万。乳腺癌死亡共415例,粗死亡率为5.43/10万,城市6.66/10/10万,农村4.18/10万;标化死亡率为4.23/10万,城市5.15/10万,农村3.25/10万。发病死亡均为城市高于农村。2009-2011年发病(χ2=94.57,P<0.001)和死亡(χ2=8.66,P<0.001)均呈现逐年增加趋势。分年龄组分析,乳腺癌发病呈单峰分布,高峰在55~岁年龄组;死亡则呈双峰分布,高峰分别在55~岁年龄组及80~岁年龄组,最高峰在55~岁年龄组。结论淮安区城市乳腺癌发病和死亡均高于农村,并呈现逐年上升趋势,发病和死亡最高峰均在55~岁年龄组,严重威胁淮安地区中老年女性的生命健康。     

Birth weight and risk of breast cancer in a cohort of 106,504 women

The possible association between prenatal factors and breast cancer has been discussed for more than a decade. Birth weight has been used commonly as a proxy measure for intrauterine growth. Whereas some previous studies have found support for an association between birth weight and breast cancer, others have been inconclusive or found no association. We investigated the relationship between birth weight and risk of female breast cancer in a cohort of 106,504 Danish women. Birth weights were obtained from school health records on girls born between 1930-1975. Information on breast cancer came from linking the cohort with the Danish Cancer Registry and the Danish Breast Cancer Cooperative Groups Registry. A total of 2,334 cases of primary breast cancer were diagnosed in the cohort during 3,255,549 person-years of follow-up among women with birth weight between 500-6,000 g. Of these, 922 (40%) were diagnosed with primary breast cancer at the age of 50 years or older. A significant association between birth weight and breast cancer was found equivalent to an increase in risk of 9% per 1,000 g increase in birth weight (95% CI 2-17). The increase was observed for all age groups, representing both pre- and post-menopausal women, and irrespective of tumor characteristics. Adjustment for age at first birth and parity did not influence the results. Birth weight is positively associated with risk of breast cancer, indicating that prenatal factors are important in the etiology of breast cancer.     

Time from breast cancer diagnosis to therapeutic surgery and breast cancer prognosis: A population‐based cohort study

Theoretically, time from breast cancer diagnosis to therapeutic surgery should affect survival. However, it is unclear whether this holds true in a modern healthcare setting in which breast cancer surgery is carried out within weeks to months of diagnosis. This is a population‐ and register‐based study of all women diagnosed with invasive breast cancer in the Stockholm‐Gotland healthcare region in Sweden, 2001–2008, and who were initially operated. Follow‐up of vital status ended 2014. 7,017 women were included in analysis. Our main outcome was overall survival. Main analyses were carried out using Cox proportional hazards models. We adjusted for likely confounders and stratified on mode of detection, tumor size and lymph node metastasis. We found that a longer interval between date of morphological diagnosis and therapeutic surgery was associated with a poorer prognosis. Assuming a linear association, the hazard rate of death from all causes increased by 1.011 (95% CI 1.006–1.017) per day. Comparing, for example, surgery 6 weeks after diagnosis to surgery 3 weeks after diagnosis, thereby confers a 1.26‐fold increased hazard rate. The increase in hazard rate associated with surgical delay was strongest in women with largest tumors. Whilst there was a clear association between delays and survival in women without lymph node metastasis, the association may be attenuated in subgroups with increasing number of lymph node metastases. We found no evidence of an interaction between time to surgery and mode of detection. In conclusion, unwarranted delays to primary treatment of breast cancer should be avoided.     

Childhood and adult milk consumption and risk of premenopausal breast cancer in a cohort of 48,844 women - the Norwegian women and cancer study

The belief that life stress enhances breast cancer is common, but there are few prospective epidemiological studies on the relationship of life stress and breast cancer. We have investigated the association between stress of daily activities (SDA) and breast-cancer risk in a prospective cohort study of 10,519 Finnish women aged 18 years or more. SDA measures a subject's own appraisal of daily stress. It was assessed in 1975 and 1981 by a self-administered questionnaire, which also provided information on subject characteristics and other known breast-cancer risk factors. Follow-up data for breast cancer from 1976 to 1996 were attained through record linkage to the Finnish Cancer Registry. Study subjects were divided into 3 groups based on their SDA scores in 1975: no stress (23% of subjects), some stress (68%) and severe stress (9%). Hazard ratios (HRs) and respective 95% confidence intervals (CIs) for incidence of breast cancer by level of SDA were obtained from the Cox proportional hazards model. We identified 205 incident breast cancers in the cohort. Multivariable-adjusted HRs for breast-cancer risk were 1.00 (reference), 1.11 (95% CI 0.78-1.57) and 0.96 (95% CI 0.53-1.73) by increasing level of stress. Neither shifting of the SDA cut-off points nor restricting the analysis to women who reported the same level of SDA in 1975 and 1981 materially altered the results. We found no evidence of an association between self-perceived daily stress and breast-cancer risk.