The impact of body mass index on breast cancer incidence among women at increased risk: an observational study from the International Breast Intervention Studies

Abstract

Background We investigated the association between body mass index (BMI) and breast cancer risk in women at increased risk of breast cancer receiving tamoxifen or anastrozole compared with placebo using data from the International Breast Cancer Intervention Studies [IBIS-I (tamoxifen) and IBIS-II (anastrozole)]. Methods Baseline BMI was calculated from nurse assessed height and weight measurements for premenopausal (n = 3138) and postmenopausal (n = 3731) women in IBIS-I and postmenopausal women in IBIS-II (n = 3787). The primary endpoint was any breast cancer event (invasive and ductal carcinoma in situ). We used Cox proportional hazards regression to calculate hazard ratios (HRs) for risk after adjustment for covariates. Results There were 582 (IBIS-I) and 248 (IBIS-II) breast cancer events [median follow-up = 16.2 years (IQR 14.4–17.7) and 10.9 years (IQR 8.8–13.0), respectively]. In adjusted analysis, women with a higher BMI had an increased breast cancer risk in both IBIS-I [HR = 1.06 per 5 kg/m2 (0.99–1.15), p = 0.114] and in IBIS-II [HR per 5 kg/m2 = 1.21 (1.09–1.35), p < 0.001]. In IBIS-I, the association between BMI and breast cancer risk was positive in postmenopausal women [adjusted HR per 5 kg/m2 = 1.14 (1.03–1.26), p = 0.01] but not premenopausal women [adjusted HR per 5 kg/m2 = 0.97 (0.86–1.09), p = 0.628]. There was no interaction between BMI and treatment group for breast cancer risk in either IBIS-I (p = 0.62) or IBIS-II (p = 0.55). Conclusions Higher BMI is associated with greater breast cancer risk in postmenopausal women at increased risk of the disease, but no effect was observed in premenopausal women. The lack of interaction between BMI and treatment group on breast cancer risk suggests women are likely to experience benefit from preventive therapy regardless of their BMI. Trial registration Both trials were registered [IBIS-I: ISRCTN91879928 on 24/02/2006, retrospectively registered (http://www.isrctn.com/ISRCTN91879928); IBIS-II: ISRCTN31488319 on 07/01/2005, retrospectively registered (http://www.isrctn.com/ISRCTN31488319)]

Association of the Interaction Between Mammographic Breast Density, Body Mass Index, and Menopausal Status With Breast Cancer Risk Among Korean Women

“… 3 , 19 Although increased adiposity was not associated with premenopausal breast cancer risk, it showed a strong association with an increased risk of postmenopausal breast cancer, which was also found in our study. 20 , 21 …”

“…3,19 Although increased adiposity was not associated with premenopausal breast cancer risk, it showed a strong association with an increased risk of postmenopausal breast cancer, which was also found in our study. 20,21 Previous studies on the interactive associations between breast density and BMI with breast cancer risk provide mixed evidence. A case-control study found that women with a breast density of 76% to 100% had a 5-fold higher risk of breast cancer than those with a breast density of 0% to 10%; moreover, breast density had a significant multiplicative interaction with BMI.…”

Mammographic breast density, body mass index and risk of breast cancer in Korean women aged 75 years and older

“…The obesity prevalence in older Korean women has gradually increased over the last decades, and the proportion of older women (aged 70 years or older) with a body mass index (BMI) of ≥25 increased from 30% in 1998 to 37% in 2019 9 . As frequently indicated by high BMI, adiposity is positively associated with increased breast cancer risk in postmenopausal women 10‐12 . The combined effect of breast density and BMI has been strongly associated with postmenopausal breast cancer risk, 6,13‐15 taking into account the interaction between these two factors.…”

“…9 As frequently indicated by high BMI, adiposity is positively associated with increased breast cancer risk in postmenopausal women. [10][11][12] The combined effect of breast density and BMI has been strongly associated with postmenopausal breast cancer risk, 6,[13][14][15] taking into account the interaction between these two factors.…”

Toward Understanding the Etiology of Male Breast Cancer: An Ongoing Research Challenge

“…Moreover, there is evidence that the rising rates of male obesity and increasing incidence of male breast cancer show parallel trends ( 6 ), although it is unclear if the two are linked. In female breast cancer, there is strong evidence that higher body mass index (BMI) and greater central adiposity are associated with increased risk of postmenopausal breast cancer, with heterogeneity by breast cancer subtype and underlying familial risk ( 5 , 7-9 ). In contrast, the evidence for obesity and male breast cancer is very limited but, based on smaller studies that examined BMI, not central adiposity or the associations by tumor subtype.…”