STAT5A and breast carcinoma: We previously showed that SH-4-54, which is able to block both phospho-STAT3 and phospho-STAT5, induces rapid ROS production in human breast cancer cells (within 4 hours of treatment), and that increases in SH-4-54-induced xCT promoter activity may be abolished by pre-treating MDA-MB-231 cells with N-acetylcysteine.