Consumption of red and processed meat and breast cancer incidence: A systematic review and meta-analysis of prospective studies.

Prior studies on red and processed meat consumption with breast cancer risk have generated inconsistent results. We performed a systematic review and meta-analysis of prospective studies to summarize the evidence regarding the relation of red meat and processed meat consumption with breast cancer incidence. We searched in MEDLINE and EMBASE databases through January 2018 for prospective studies that reported the association between red meat and processed meat consumption with incident breast cancer. The multivariable-adjusted relative risk (RR) was combined comparing the highest with the lowest category of red meat (unprocessed) and processed meat consumption using a random-effect meta-analysis. We identified 13 cohort, 3 nested case-control and two clinical trial studies. Comparing the highest to the lowest category, red meat (unprocessed) consumption was associated with a 6% higher breast cancer risk (pooled RR,1.06; 95% confidence intervals (95%CI):0.99-1.14; I2 = 56.3%), and processed meat consumption was associated with a 9% higher breast cancer risk (pooled RR, 1.09; 95%CI, 1.03-1.16; I2 = 44.4%). In addition, we identified two nested case-control studies evaluating the association between red meat and breast cancer stratified by N-acetyltransferase 2 acetylator genotype. We did not observe any association among those with either fast (per 25 g/day pooled odds ratio (OR), 1.18; 95%CI, 0.93-1.50) or slow N-acetyltransferase 2 acetylators (per 25 g/day pooled OR, 0.99; 95%CI, 0.91-1.08). In the prospective observational studies, high processed meat consumption was associated with increased breast cancer risk.