p53 status but not cancer cell type is a critical indicator for bortezomib sensitivity. Lung cancer cell lines (A, EKVX with mutant p53 and A549 with wild type p53), breast cancer cell lines (B, MDA-MB-231 with mutant p53 and MCF-7 with wild type p53), prostate cancer cell lines (C, PC-3 with null p53 and LNCaP with wild type p53) and myeloma cancer cell lines (D, RPMI-8226 with mutant p53 and KMS11 with wild type p53) were seeded in 96-well cell cultural plates at 30% confluence. Cells were treated with and without a series of bortezomib concentrations for 48 hours 16 hours after seeding. Cell growth/survival was then determined by MTT assay. The resultant data were represented in histograms. Each bar is the mean ± SD derived from three independent determinations.