CCDC170 and Fibroadenoma: In none of these cases did we detect an ESR1 fusion transcripts with AKAP12 or ARMT1. However, one of the breast tissues of women without breast cancer diagnosis (10%) showed ESR1-CCDC170 exon 2 (E2-E2) fusion transcripts, one of the DCIS cases (7.7%) had ESR1-CCDC170 exon 6 (E2-E6) fusion transcripts, and four patients with fibroadenoma (25%) had ESR1-CCDC170 exon 8 (E2-E8) fusion transcripts (Table 4 and Additional file 6).