The assay cannot be applied to all cell lines, since some do not metabolize MTT (for example, breast cancer cell lines VACC 732 and VACC 812) and some lose the ability to do so at high density (for example, colon carcinoma cell line HCT-8). (31,32) The absorbance at 570 nm which is directly related to the level of the product, MTT formazan, varies significantly among different cell lines; therefore, assay conditions for each cell line should be initially established before a detailed use of this method.