Subsequently, subgroups (within major groups) that have been defined as ER-, PR-, and HER2- tumors that express cytokeratin (CK) 5/6 proteins or epidermal growth factor receptor (EGFR) or both represent another distinctive BC tumor subtype known as the core basal phenotype, which is associated with a worse prognosis [6]. This evidence concerns the gene EGFR and breast cancer.