AKT1 and neoplasm: 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).