BCL2 and breast cancer: In addition, miR-503 has also been described as part of a miRNA cluster, known as miR-424(322)/503, whose loss in breast cancer patients has been associated with the development of aggressive breast cancer, and also found to promote paclitaxel resistance in vivo due to the increased expression of two of their targets: BCL-2 (B-cell lymphoma 2) and IGF1R (insulin-like growth factor-1 receptor) [59].