Risk factors for metachronous contralateral breast cancer: A systematic review and meta-analysis

•BC patients with a BRCA1, BRCA2 or CHEK2 c.1100delC mutation are at high risk for a CBC.•Family history for BC, or a high BMI are both relevant risk factors for CBC.•Lobular histology or ER negative receptor status of a primary BC are tumor-related risk factors for a CBC.•Treatment of a primary BC with radiotherapy before age 40 is associated with an increased risk of CBC.•Adjuvant treatment with chemotherapy or endocrine therapy is associated with a decreased risk of CBC.