Somatic mutations are present in all members of the AKT family in endometrial carcinoma

Sir,

The activating E17K mutations recently discovered in the pleckstrin homology domain of AKT1 in about 2% of endometrial cancer patients (Shoji et al, 2009) suggest a new mechanism for PI3 kinase pathway activation in these patients, as previously described in breast, colorectal and ovarian cancers (Carpten et al, 2007). Additional mechanisms of PI3 kinase pathway activation in endometrial cancer include the somatic mutation of PTEN and PIK3CA (Kong et al, 1997; Oda et al, 2005), amplification and overexpression of PIK3CA (Miyake et al, 2008; Salvesen et al, 2009), and decreased expression of PTEN (Kanamori et al, 2001; Kappes et al, 2001).

We found an additional four mutations in AKT family members (Table 1). Two of these (mutations in the catalytic domain of AKT2 (D399N) and the regulatory domain of AKT3 (E438D)) were previously reported in a sequencing screen of 123 genes in 41 primary endometrial cancers (Dutt et al, 2008). Manual reinspection of these data in light of the report on activating AKT1 mutations in endometrial cancer (Shoji et al, 2009) revealed an additional mutation, AKT1 E17K, identical to the one reported by Shoji et al (2009), and a novel mutation in the catalytic domain of AKT2 (R368C) in two additional samples. We validated these mutations as somatic by mass spectrometric genotyping of the tumour and matched normal DNA, after an independent PCR amplification. We also found a novel candidate mutation in the pleckstrin homology domain of AKT2 (D32H), which we could not validate because of insufficient DNA. All these mutations occurred in cancers of the endometrioid subtype that had no signs of metastasis either at primary treatment or during follow-up. Taken together, we find that 5 out of 41 endometrial cancers have mutations in AKT family members for a 12% rate.

Table 1 AKT family mutations found in endometrial cancer

Confirmation that these novel mutations activate the PI3 kinase pathway awaits their functional characterisation. Notably, all the AKT family member mutations found in our data occur at residues conserved across multiple species (see Supplementary Figure 1). However, three of these five mutations were identified in samples harbouring mutations of PTEN, one of which also had amplification of and a mutation in PIK3CA (Table 1); the AKT1 E17K mutation is not associated with either PTEN or PIK3CA genomic alteration. It is therefore possible that these AKT family mutations have different functional effects from mutations of PTEN and PIK3CA. Given the importance of the PI3 kinase pathway in endometrial cancer oncogenesis (Salvesen et al, 2009), and the emerging therapeutic options for PI3 kinase inhibition (Garcia-Echeverria and Sellers, 2008), the functional effects of all these AKT family mutations should be investigated in appropriate model systems of endometrial cancer.