EGFR and cancer: Given this perspective, one of the most critically important mathematical variables related to cancer cell biology that can significantly determine the anti-neoplastic cytotoxicity of covalent immunochemotherapeutics like gemcitabine-[anti-HER2/neu], [19] [24] gemcitabine-[anti-EGFR], epirubicin-[anti-HER2/neu] [16] [18] [25] or epirubicin-[anti-EGFR], [16] is the expression density of “sites” on the external surface membrane of neoplastic cells utilized to facilitate the selective “targeted” delivery of chemotherapeutic moieties.