BRCA1 and breast cancer: In a previous analytical exercise exploring structural variation in breast cancer, six classes of rearrangement signatures were identified15, including two types of tandem duplication signatures—Rearrangement Signature 3 (RS3) comprising short (<10 Kb) tandem duplications and enriched in BRCA1-null tumours and Rearrangement Signature 1 (RS1) comprising long (>100 Kb) tandem duplications, not associated with BRCA1 mutations although a genetic cause has not been identified.