The notion for the mutant p53 gain-of-function theory is supported by recent studies using mutant p53 ‘knockin’ mice, which display a broader tumour spectrum, increased aggressiveness, and metastatic potential as compared with their p53-null counterparts (Hsiao et al, 1994; Liu et al, 2000; Lang et al, 2004; Olive et al, 2004). This evidence concerns the gene TP53 and neoplasm.