MUC6 and breast cancer: In a recent analysis, multiple mucins, including MUC1, MUC2, MUC5AC, and MUC6, were found to differentiate primary BC from metastatic BC, where MUC1 correlated with the low or early grade, MUC5AC with metastatic disease, and MUC6 emerged as an indicator of poor prognosis [172,173].