This hypothesis is based on our findings demonstrating that CTL induced by ACE from the Ova-4 and Ova-5 HLA-A2.1+ but HER-2/neu− primary tumours only weakly lysed their autologous tumour targets (i.e. the Ova-4 and Ova-5 primary tumours) as well as the HLA-A2.1+ and HER-2/neu+ SKOV3.A2 and MCF-7 tumour cell lines. This evidence concerns the gene ACE and neoplasm.