Adiposity, exercise, diet, and outcomes after breast cancer diagnosis: World Cancer Research Fund (WCRF)/American Institute for Cancer Research (AICR) systematic literature review and meta-analysis.
Session type: E-poster/poster
Despite improvements in breast cancer therapy and survival, evidence-based cancer survivorship-specific recommendations regarding diet, exercise and weight management have not been established. Our aim was to summarise peer-reviewed literature since the previous WCRF/AICR 2014 Continuous Update Project report and evaluate what the latest evidence shows.
We searched PubMed and Embase until 31/12/2018 for randomised controlled trials (RCTs) or longitudinal observational studies. We conducted linear and non-linear dose-response meta-analyses and investigated between-study heterogeneity and small-study effects. An Expert Panel judged the evidence using the pre-defined WCRF/AICR survivorship criteria.
Overall, 332 publications were identified. Meta-analyses were performed only for observational studies, as very few relevant RCTs were identified. Each 5 kg/m2 BMI increment was associated with a 7% (95%CI:4%-9%, I2=58%, studies=55) and 9% (95%CI:5%-13%, I2=61%, studies=39), higher risk of all-cause, breast cancer-specific mortality, respectively. The risk of second primary cancer development was 14% higher (95%CI:7%-21%, I2=5%, studies=9). Evidence was graded as “strong” to support a probable causal relationship. Each 10 MET-h/week increment of recreational physical activity was associated with a 16% and 9% lower risk of all-cause (95%CI:8%-24%, I2=84%, studies=7) and breast cancer-specific mortality (95%CI:2%-16%, I2=50%, studies=6), respectively. Non-linear analyses revealed risk reductions for all-cause and breast cancer-specific mortality with increasing exercise, reaching a plateau at ~20 MET-h/week. Evidence was graded as “limited-suggestive”. A 10 g/day increment of fibre intake was associated with a 14% lower all-cause mortality (95%CI:1%-26%, I2=0%, studies=3). Every 10 nmol/L increment in serum 25(OH)D concentration was associated with an 8% and 6% lower risk of all-cause (95%CI:5%-11%, I2=0%, studies=5) and breast cancer-specific mortality (95%CI:1%-10%, I2=24%, studies=5); this evidence was judged as “limited-suggestive”. Our analyses did not detect associations between any other dietary exposures and breast cancer prognosis, and these thus received a “limited-no-conclusion” grading.
Our findings indicate that adiposity (“strong” evidence) and physical activity (“limited-suggestive” evidence) could influence breast cancer prognosis. However, residual confounding, reverse causation and other potential biases must be considered. Large, well-designed observational studies with repeated measurements, and relevant RCTs with high compliance are necessary to clarify the impact of body composition, exercise and diet on outcomes after breast cancer diagnosis.