ABCB1 and breast cancer: Such transcriptional fusions (rearrangements) between ABCB1 and its fusion partners (e.g., SLC25A40 and CNOT4) provide ABCB1 with a more active promoter at the 5′ end of its transcript and, thus, upregulate ABCB1 expression in high-grade serous ovarian cancer (HGSC) and end-stage breast cancer patients [90].