It has also been proposed that trastuzumab resistance may be associated with decreased p27(kip1) levels (Nahta et al, 2004), or with the loss of function of the tumour-suppressor PTEN gene, the negative regulator of Akt, which results in strengthened Akt signalling, which in turn leads to decreased sensitivity to trastuzumab (Fujita et al, 2006). This evidence concerns the gene PTEN and neoplasm.