Not really a surprise, since we know there are hormonal factors and fat stores hormones. However the authors point out other contradictory studies in their background statement.
82 studies, so the problem of meta-analysis is there, but the conclusion makes some sense. The associations are not real strong, RR less than 2 but the potential confounders are not as big a problem as in other observational studies–this is just outcomes and mortality versus BMI.
Obesity seems to increase breast cancer risk.
Meta-Analysis of BMI and Survival in Breast Cancer Patients
Research · April 27, 2014
Ann. Oncol 2014 Apr 27;[EPub Ahead of Print], DS Chan, AR Vieira, D Aune, EV Bandera, DC Greenwood, A McTiernan, D Navarro Rosenblatt, I Thune, R Vieira, T Norat
In this large meta-analysis of 82 studies evaluating the association between obesity and breast cancer survival, investigators found that increased BMI before or after breast cancer diagnosis and treatment was associated with a significant increased risk of total and
breast cancer–specific mortality, in both pre- and post-menopausal women.
This systematic review sheds further light on the impact of obesity in breast cancer and illustrates the need for continued weight management before, during, and after breast cancer diagnosis and treatment.
– Chris Tully, MD
Positive association between obesity and survival after breast cancer was demonstrated in previous meta-analyses of published data, but only the results for the comparison of obese versus non-obese was summarised.
We systematically searched in MEDLINE and EMBASE for follow-up studies of breast cancer survivors with body mass index (BMI) before and after diagnosis, and total and cause-specific mortality until June 2013, as part of the World Cancer Research Fund Continuous Update Project. Random-effects meta-analyses were conducted to explore the magnitude and the shape of the associations.
Eighty-two studies, including 213 075 breast cancer survivors with 41 477 deaths (23 182 from breast cancer) were identified. For BMI before diagnosis, compared with normal weight women, the summary relative risks (RRs) of total mortality were 1.41 [95% confidence interval (CI) 1.29-1.53] for obese (BMI >30.0), 1.07 (95 CI 1.02-1.12) for overweight (BMI 25.0-<30.0) and 1.10 (95% CI 0.92-1.31) for underweight (BMI <18.5) women. For obese women, the summary RRs were 1.75 (95% CI 1.26-2.41) for pre-menopausal and 1.34 (95% CI 1.18-1.53) for post-menopausal breast cancer. For each 5 kg/m(2) increment of BMI before, <12 months after, and ≥12 months after diagnosis, increased risks of 17%, 11%, and 8% for total mortality, and 17%, 18%, and 29% for breast cancer mortality were observed, respectively.
Obesity is associated with poorer overall and breast cancer survival in pre- and post-menopausal breast cancer, regardless of when BMI is ascertained. Being overweight is also related to a higher risk of mortality. Randomised clinical trials are needed to test interventions for weight loss and maintenance on survival in women with breast cancer.
Annals of Oncology
Body Mass Index and Survival in Women With Breast Cancer–Systematic Literature Review and Meta-Analysis of 82 Follow-Up Studies