Body mass index, tumor characteristics, and prognosis following diagnosis of early-stage breast cancer in a mammographically screened population

Abstract

Purpose Many studies suggest increased body mass index (BMI) is associated with worse breast cancer outcomes, but few account for variability in screening, access to treatment, and tumor differences. We examined the association between BMI and risk of breast cancer recurrence, breast cancer-specific mortality, and all-cause mortality, and evaluated whether tumor characteristics differ by BMI among a mammographically-screened population with access to treatment. Methods Using a retrospective cohort study design, we followed 485 women aged ≥40 years diagnosed with stage I/II breast cancer within 24 months of a screening mammogram occurring between 1988 and 1993 for 10-year outcomes. BMI before diagnosis was categorized as normal (<25 kg/m2), overweight (25–29.9 kg/m2), and obese (≥30 kg/m2). Tumor marker expression was assessed via immunohistochemistry using tissue collected before adjuvant treatment. Medical records were abstracted to identify treatment, recurrence, and mortality. We used Cox proportional hazards to separately model the hazard ratios (HR) of our three outcomes by BMI while adjusting for age, stage, and tamoxifen use. Results Relative to normal weight women, obese women experienced increased risk of recurrence (HR-2.43; 95%CI-1.34–4.41) and breast cancer death (HR-2.41; 95%CI-1.00–5.81) within 10 years of diagnosis. There was no association between BMI and all-cause mortality. Obese women had significantly faster growing tumors, as measured by Ki-67. Conclusions Our findings add to the growing evidence that obesity may contribute to poorer breast cancer outcomes, and also suggest that increased tumor proliferation among obese women is a pathway that explains part of their excess risk of adverse outcomes.

Obesity as an independent risk factor for decreased survival in node-positive high-risk breast cancer

“…A retrospective analysis of patients enrolled in the randomized Phase-III BIG 02-98 trial reported that obesity was associated with poorer outcome independently from other prognostic factors [19]. In contrast, a recent pooled analysis of two randomized French trials found no significant influence of obesity on DFS or OS after adjusting for tumor characteristics [20]. Both studies differed from our study with regard to the number of positive lymph nodes of patients included; while the majority of patients in these two studies had only 1-3 positive lymph nodes, our study comprised only high-risk patients with more than 3 positive lymph nodes.…”

“…Both studies differed from our study with regard to the number of positive lymph nodes of patients included; while the majority of patients in these two studies had only 1-3 positive lymph nodes, our study comprised only high-risk patients with more than 3 positive lymph nodes. Nevertheless, the reason for the lack of a significant negative effect of obesity on breast cancer prognosis in the French population remains unclear, and the authors could only speculate that local dietary habits and/or types and intensities of adjuvant chemotherapies might reduce the negative impact of obesity [20].…”

Obesity and breast cancer: role of inflammation and aromatase

“…BMI is routinely used to quantify adiposity. In the case of breast cancer, a BMI of 30 kg/m 2 carries with it a twofold increased risk compared with a 'normal' BMI of 24-25, and the risk continues to increase with increased obesity (Biglia et al 2012, Garrisi et al 2012, Kamineni et al 2012. Breast cancer risk increases with ageing and the relationship with BMI appears to apply primarily to postmenopausal women.…”

Breast cancer outcomes in a population with high prevalence of obesity

“…There was no association between obesity and breast cancer recurrence among patients treated within the NSABP B-14 trial [11]. Some authors have postulated that the results of most observational studies on obesity and breast cancer outcomes are related to the adequacy of therapy and intensity of surveillance, which are tightly controlled in clinical trials such as the B-14 trial [6]. The treatment and surveillance protocol at our institution may have similar intensity to clinical trials, therefore resulting in a mitigation of the effect on prognosis seen in most observational studies.…”