SummaryBackgroundMenarche and menopause mark the onset and cessation, respectively, of ovarian activity associated with reproduction, and affect breast cancer risk. Our aim was to assess the strengths of their effects and determine whether they depend on characteristics of the tumours or the affected women.MethodsIndividual data from 117 epidemiological studies, including 118 964 women with invasive breast cancer and 306 091 without the disease, none of whom had used menopausal hormone therapy, were included in the analyses. We calculated adjusted relative risks (RRs) associated with menarche and menopause for breast cancer overall, and by tumour histology and by oestrogen receptor expression.FindingsBreast cancer risk increased by a factor of 1·050 (95% CI 1·044–1·057; p<0·0001) for every year younger at menarche, and independently by a smaller amount (1·029, 1·025–1·032; p<0·0001), for every year older at menopause. Premenopausal women had a greater risk of breast cancer than postmenopausal women of an identical age (RR at age 45–54 years 1·43, 1·33–1·52, p<0·001). All three of these associations were attenuated by increasing adiposity among postmenopausal women, but did not vary materially by women's year of birth, ethnic origin, childbearing history, smoking, alcohol consumption, or hormonal contraceptive use. All three associations were stronger for lobular than for ductal tumours (p<0·006 for each comparison). The effect of menopause in women of an identical age and trends by age at menopause were stronger for oestrogen receptor-positive disease than for oestrogen receptor-negative disease (p<0·01 for both comparisons).InterpretationThe effects of menarche and menopause on breast cancer risk might not be acting merely by lengthening women's total number of reproductive years. Endogenous ovarian hormones are more relevant for oestrogen receptor-positive disease than for oestrogen receptor-negative disease and for lobular than for ductal tumours.FundingCancer Research UK.

SummaryBackgroundPublished findings on breast cancer risk associated with different types of menopausal hormone therapy (MHT) are inconsistent, with limited information on long-term effects. We bring together the epidemiological evidence, published and unpublished, on these associations, and review the relevant randomised evidence.MethodsPrincipal analyses used individual participant data from all eligible prospective studies that had sought information on the type and timing of MHT use; the main analyses are of individuals with complete information on this. Studies were identified by searching many formal and informal sources regularly from Jan 1, 1992, to Jan 1, 2018. Current users were included up to 5 years (mean 1·4 years) after last-reported MHT use. Logistic regression yielded adjusted risk ratios (RRs) comparing particular groups of MHT users versus never users.FindingsDuring prospective follow-up, 108 647 postmenopausal women developed breast cancer at mean age 65 years (SD 7); 55 575 (51%) had used MHT. Among women with complete information, mean MHT duration was 10 years (SD 6) in current users and 7 years (SD 6) in past users, and mean age was 50 years (SD 5) at menopause and 50 years (SD 6) at starting MHT. Every MHT type, except vaginal oestrogens, was associated with excess breast cancer risks, which increased steadily with duration of use and were greater for oestrogen-progestagen than oestrogen-only preparations. Among current users, these excess risks were definite even during years 1–4 (oestrogen-progestagen RR 1·60, 95% CI 1·52–1·69; oestrogen-only RR 1·17, 1·10–1·26), and were twice as great during years 5–14 (oestrogen-progestagen RR 2·08, 2·02–2·15; oestrogen-only RR 1·33, 1·28–1·37). The oestrogen-progestagen risks during years 5–14 were greater with daily than with less frequent progestagen use (RR 2·30, 2·21–2·40 vs 1·93, 1·84–2·01; heterogeneity p<0·0001). For a given preparation, the RRs during years 5–14 of current use were much greater for oestrogen-receptor-positive tumours than for oestrogen-receptor-negative tumours, were similar for women starting MHT at ages 40–44, 45–49, 50–54, and 55–59 years, and were attenuated by starting after age 60 years or by adiposity (with little risk from oestrogen-only MHT in women who were obese). After ceasing MHT, some excess risk persisted for more than 10 years; its magnitude depended on the duration of previous use, with little excess following less than 1 year of MHT use.InterpretationIf these associations are largely causal, then for women of average weight in developed countries, 5 years of MHT, starting at age 50 years, would increase breast cancer incidence at ages 50–69 years by about one in every 50 users of oestrogen plus daily progestagen preparations; one in every 70 users of oestrogen plus intermittent progestagen preparations; and one in every 200 users of oestrogen-only preparations. The corresponding excesses from 10 years of MHT would be about twice as great.FundingCancer Research UK and the Medical Research Council.

Alcohol and tobacco consumption are closely correlated and published results on their association with breast cancer have not always allowed adequately for confounding between these exposures. Over 80% of the relevant information worldwide on alcohol and tobacco consumption and breast cancer were collated, checked and analysed centrally. Analyses included 58 515 women with invasive breast cancer and 95 067 controls from 53 studies. Relative risks of breast cancer were estimated, after stratifying by study, age, parity and, where appropriate, women's age when their first child was born and consumption of alcohol and tobacco. The average consumption of alcohol reported by controls from developed countries was 6.0 g per day, i.e. about half a unit/drink of alcohol per day, and was greater in ever-smokers than never-smokers, (8.4 g per day and 5.0 g per day, respectively). Compared with women who reported drinking no alcohol, the relative risk of breast cancer was 1.32 (1.19 -1.45, P50.00001) for an intake of 35 -44 g per day alcohol, and 1.46 (1.33 -1.61, P50.00001) for 545 g per day alcohol. The relative risk of breast cancer increased by 7.1% (95% CI 5.5 -8.7%; P50.00001) for each additional 10 g per day intake of alcohol, i.e. for each extra unit or drink of alcohol consumed on a daily basis. This increase was the same in ever-smokers and never-smokers (7.1% per 10 g per day, P50.00001, in each group). By contrast, the relationship between smoking and breast cancer was substantially confounded by the effect of alcohol. When analyses were restricted to 22 255 women with breast cancer and 40 832 controls who reported drinking no alcohol, smoking was not associated with breast cancer (compared to never-smokers, relative risk for ever-smokers=1.03, 95% CI 0.98 -1.07, and for current smokers=0.99, 0.92 -1.05). The results for alcohol and for tobacco did not vary substantially across studies, study designs, or according to 15 personal characteristics of the women; nor were the findings materially confounded by any of these factors. If the observed relationship for alcohol is causal, these results suggest that about 4% of the breast cancers in developed countries are attributable to alcohol. In developing countries, where alcohol consumption among controls averaged only 0.4 g per day, alcohol would have a negligible effect on the incidence of breast cancer. In conclusion, smoking has little or no independent effect on the risk of developing breast cancer; the effect of alcohol on breast cancer needs to be interpreted in the context of its beneficial effects, in moderation, on cardiovascular disease and its harmful effects on cirrhosis and cancers of the mouth, larynx, oesophagus and liver. Many epidemiological studies have investigated the relationship between breast cancer and the consumption of alcohol and/or tobacco. References to over 80 studies that have collected relevant data, as well as to reviews of the subject, are given in Appendix II (www. bjcancer.com). The published results from these studies have general...

Numerous epidemiologic studies have found body size to be a significant risk factor in the etiology of breast cancer. In an Israeli study population of 1,065 breast cancer patients, 964 surgical controls, and 981 neighborhood controls, height and weight at three periods (age 18, "most of adult life," and recent) were ascertained. The authors analyzed these parameters and body mass index (weight/height) for each period, as well as body mass index changes throughout life, controlling for age, menstrual status, and ethnic origin. Odds ratios were determined for three body mass index categories: 19.1-23, 23.1-27, and 27.1+, with a relative risk of 1 for body mass index less than or equal to 19. Their results show an increase in risk for breast cancer with greater recent body mass index among postmenopausal women aged 60+ (n = 461 for breast cancer, n = 414 for surgical controls, n = 401 for neighborhood controls). Crude odds ratios for the breast cancer/surgical control comparison are 1.23, 1.58, and 2.20, respectively, for each body mass index category; for the breast cancer/neighborhood control comparison 2.16, 2.44, and 2.99, respectively. Odds ratios adjusted for confounding factors (ages at menarche, first birth, and menopause; number of births; years of education; previous benign breast disease; and family history of breast cancer) are 1.17, 1.44, and 2.38, respectively (breast cancer/surgical control); and 1.78, 1.92, and 2.53, respectively (breast cancer/neighborhood control). Overweight does not emerge as a risk factor for breast cancer among premenopausal or younger postmenopausal women. Weight loss from most of adult life to recent weight appears to be protective, since mean loss in the 60+ age category is greater in both control groups than in breast cancer patients. In addition, breast cancer patients aged 60+ gained more weight during adult life than controls, and premenopausal breast cancer patients gained less weight than controls (for both comparisons, p less than or equal to 0.05, breast cancer vs. all controls combined.

A case-control study of 818 breast cancer (BC) patients and 2 matched control groups, surgical controls (SCs) and neighborhood controls (NCs), was undertaken in Israel between 1975 and 1978. The interview schedule included a detailed dietary history based on the frequency of consumption of 250 food items, which were grouped according to their principal nutrient component. The average frequency of consumption of each food item in each nutrient group was computed. Medical, demographic, hormonal, and parity histories were also obtained. Risks associated with fat, animal protein, and fiber consumption were evaluated. Two types of analysis were performed [in 2 age groups (less than 50 yr and greater than or equal to 50 yr)], using the conditional logistic method: evaluating the risk attributable to nutrition only and controlling for nondietary confounding factors as well. When no adjustment for nondietary confounding factors was made, the risk increased with fat intake in both age groups [one-tailed P-value for linear trend = .08 and .07 in age less than 50 and .01 and .10 for the greater than or equal to 50 age category for the BC case (BCC)-SC and BCC-NC comparisons, respectively]. Increased fiber intake decreased the risk in the younger age group (one-tailed P-value for linear trend = .06 and .07 for the BCC-SC and BCC-NC comparisons, respectively), while in the 50-or-over age category the trend was inconsistent. The risk associated with animal protein was much less clear. For women in the highest quartiles of fat and animal protein intake and the lowest quartiles of fiber intake, risk was about twice as high as that for women in the lowest quartiles of fat and animal protein intake and in the highest quartile of fiber intake (one-tailed P-value for linear trend = .04 and .08 for age less than 50 and .08 and .09 for the age category greater than or equal to 50 BCC-SC and BCC-NC comparisons, respectively). When hormonal and demographic confounding factors were controlled for, this pattern persisted but it remained significant for 1 control only. Power increased when cases were analyzed against both controls simultaneously (one-tailed P-value for linear trend = .10 for age less than 50 and .02 for age greater than or equal to 50). Thus a higher fat-animal protein and lower fiber diet is associated with increased cancer risk, but this relationship needs to be studied further.