BRCA1 and neoplasm: However, individual variations occurred; the most pronounced were: (i) for BRCA1, circRNA_23-20, with an increase in relative proportion from 2.71% in the normal tissue to 5.51% in the tumor tissue and circRNA_3-2 with a decrease from 5.42% in the normal tissue to 2.17% in the tumor tissue; (ii) for BRCA2, the novel circRNA 26-13 dropped from 4.26% in the normal tissue to 0.67% in the tumor tissue.