The purpose of the current study was to determine the impact of cancer cell enlargement on chemosensitivity as measured by multiwell plate colorimetric (XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilid)) and fluorimetric (CellTiter-Blue) assays in the human cancer cell lines A549 (lung carcinoma) and MDA–MB-231 (breast carcinoma), which express wild-type and mutant p53, respectively. The gene discussed is TP53; the disease is breast carcinoma.