MUC1 and breast cancer: The difficulty of predicting the BC prognosis among a complex tumor microenvironment comprised of molecular and cellular heterogeneity between some commonly used markers in several cancers, such as CA 15-3, CA 27.29, CEA, MUC1, MUC16, TP53, FOXM1, ER, PR, HER2, KI 67, and others (Børresen-Dale, 2003; Lakshmanan et al., 2012; Graham et al., 2014; Kabel, 2017; Song et al., 2017; Stergiou et al., 2019), makes a prediction inaccurate.