The impact of lifestyle and reproductive factors on the risk of a second new primary cancer in the contralateral breast: a systematic review and meta-analysis

Purpose The risk of being diagnosed with contralateral breast cancer (CBC) is an important health issue among breast cancer survivors. There is an increasing interest in the effect of lifestyle and reproductive factors on CBC risk, since these factors may partly be modifiable. We performed a systematic review and meta-analysis and aimed to evaluate the impact of lifestyle and reproductive factors on CBC risk in population-based breast cancer studies. Methods The PubMed electronic database was searched up to 2nd November 2019, for relevant publications. Of the included studies, a meta-analysis per lifestyle or reproductive factor was performed. Results Thirteen out of 784 publications were used for the meta-analysis. Body mass index (≥ 25 vs.