Among the many target genes of miR-124, signal transducer and activator of transcription 3 (STAT3) is the most popular gene shared by many types of cancer cells and is reportedly a target gene in glioma [39], lung cancer [32,55,63,65], colorectal cancer [75,76], hepatocellular carcinoma [80], breast cancer [97,100], endometrial cancer [101], esophageal cancer [102,103], nasopharyngeal carcinoma [104], retinoblastoma [105], prostate cancer [106], and cholangiocarcinoma [107]. This evidence concerns the gene STAT3 and breast cancer.