MUC1 and breast cancer: Several mucins have shown clinical promise, including MUC1 (also known as CA 15-3 and KL-6, in breast cancer [13,15]), MUC4 (pancreatic cancer [16]), and MUC5 (gastrointestinal, pancreatic, gastric cancers [13,17,18]); however, only one is FDA-approved and in clinical use, MUC16, also known as CA125 in ovarian cancer [19,20].