ESR1 and breast cancer: Furthermore, immunohistochemical and meta-analysis studies performed in breast cancer have demonstrated that increased FAK levels are associated with a high mitotic index, nuclear and architectural grade 3, ER and PR negativity, HER2 overexpression, TNBC phenotype and high Ki-67 levels, whereas no significant correlations were identified between FAK expression and age, lymph node infiltration and tumor size [15,17].