Research Findings

Incidence Studies - Breast Cancer

Association of Body Mass Index and Age With Subsequent Breast Cancer Risk in Premenopausal Women (2018)
 In a pooled analysis of individual data for 758,592 premenopausal women from 19 international cohort studies, risk for premenopausal breast cancer (13,082 cases) decreased significantly with increasing body mass index (BMI) at ages 18-24, 25-34, 35-44, and 45-54. The inverse association was stronger for BMI at younger versus older ages and for hormone receptor-positive versus hormone receptor-negative tumors, but did not differ substantially by attained age or with adjustment for other breast cancer risk factors.
The Premenopausal Breast Cancer Collaboration: A Pooling Project of Studies Participating in the National Cancer Institute Cohort Consortium (2017)
 The Premenopausal Breast Cancer Collaborative Group was created to evaluate risk factors for premenopausal breast cancer by pooling data from 20 U.S. cohort studies participating in the National Cancer Institute Cohort Consortium. This article describes the individual cohorts and study objectives.
Breast cancer risk and protracted low-to-moderate dose occupational radiation exposure in the US Radiologic Technologists Cohort, 1983–2008 (2016)
 Breast cancer incidence (1,922 cases) and mortality (586 deaths) increased with increasing radiation dose to the breast in female radiologic technologic. Risks were most pronounced in women who were born before 1930 and began working before 1950, when the doses were considerably higher.
Prospective study of ultraviolet radiation exposure and risk of breast cancer in the United States (2016)
 Breast cancer risk (716 cases) among 36,725 female radiologic technologists was not related to measures of solar ultraviolet radiation (UVR) exposure, including ambient UVR calculated by linking satellite-based annual UVR estimates to self-reported residential histories, time spent outdoors, and a combined index. Risk was also unrelated to skin complexion, eye or hair color, and sunburn history.
Menarche, menopause, and breast cancer risk: individual participant meta-analysis, including 118,964 women with breast cancer from 117 epidemiological studies (2012)
 Based on a meta-analysis that included 118,964 women with breast cancer from 117 epidemiological studies, breast cancer risk increased significantly with earlier age at menarche and later age at menopause, and was higher in premenopausal than post-menopausal women. Risks were also examined by sociodemographic, personal, and tumor characteristics.
Hormone-related risk factors and postmenopausal breast cancer among nulliparous vs parous women: an aggregated study (2011)
 Nulliparity is an established breast cancer risk factor, especially when compared with parity at young ages. The authors aggregated data from four prospective studies including 32,641 nulliparous (1,612 breast cancers) and 204,270 parous women (8,180 breast cancers) to examine the hypothesis that nulliparity may increase susceptibility to established postmenopausal breast cancer risk factors. One of the studies included in the aggregated report was the USRT cohort study. The results suggested that breast cancer risk from common hormonal factors does not differ by parity.
Physical activity and breast cancer risk among pre- and postmenopausal women in the U.S. Radiologic Technologists cohort (2009)
 We evaluated physical activity in relation to breast cancer risk among 45,631 female radiologic technologists who completed a baseline and follow-up questionnaire. There were 864 women who reported breast cancer. We found that breast cancer risk decreased with increasing physical activity, with the greatest reductions in risk observed for walking or hiking for exercise among premenopausal women and postmenopausal women who never used menopausal hormone therapy. Breast cancer risk was modestly reduced at the highest levels of strenuous exercise and walking at home or work.
Smoking cigarettes before first childbirth increases risk of breast cancer (2007)
 We evaluated breast cancer risk associated with cigarette smoking during different periods of reproductive life among radiologic technologists who completed the first and second study questionnaires. After accounting for age, birth cohort, and established breast cancer risk factors, we found that smoking-related breast cancer risks differed by smoking during three reproductive time periods, with a statistically significant 3% increase per pack-year smoked between menarche and first childbirth and no significant association for smoking after first childbirth. Risk also increased with younger age started smoking.
Breast cancer incidence in U.S. radiologic technologists (2006)
 Among female radiologic technologists who completed the first and second study questionnaires, 1050 new breast cancers occurred between 1983 and 1998. We evaluated breast cancer risk according to employment characteristics and a 4-level proxy index for cumulative radiation exposure. Women who began working as a radiologic technologist before 1940 had a statistically significant 2-fold risk compared to women who began working in 1970 or later, and risk increased significantly with increasing number of years worked before 1940. Breast cancer risk was not related to working as a radiologic technologist in the 1940s or later. Women in the highest exposure group (level 4) had a 50% greater breast cancer risk than those in the lowest exposure group.
Breast cancer among radiologic technologists (letter) (1996)
Breast cancer among radiologic technologists (1995)
 Among 79,000 female radiologic technologists who completed the first survey in the mid-1980s, 528 technologists reported an eligible breast cancer. We compared the 528 breast cancer cases with a similar group of 2,628 technologists who did not have breast cancer. Consistent with other studies, we found higher breast cancer risks for technologists who started menstruating at an early age (<11), never had children, had a first-degree family relative with breast cancer, had a prior breast biopsy (at least one year before breast cancer diagnosis), consumed more than 14 alcoholic drinks per week, and resided in the northeastern United States. Breast cancer risk was not related to total number of years worked as a radiologic technologist, nor with jobs involving radiotherapy, radioisotopes, or fluoroscopy. Personal medical radiation exposures from fluoroscopic or multi-film procedures also did not affect risk.
Employment practices and breast cancer among radiologic technologists (1995)
 In further analyses, we found that breast cancer risk did not differ according to the types of procedures radiologic technologists performed or the number of years they worked with these procedures. The procedures that we evaluated were fluoroscopy, portable radiograph, routine radiograph, multi-film procedure, dental x-ray, radium therapy, orthovoltage, cobalt-60, betatron, other radiograph teletherapy, other radioisotope therapy, diagnostic radioisotope, microwave/ultrasound diathermy, diagnostic ultrasound, and CAT scan.