PTEN and colorectal neoplasm: The identification of only one tumour with a PTEN mutation in our series of MSI− tumours, consistent with the recent results of Zhou et al (2002), indicates that the inactivation of PTEN by mutation is a rare event in MSI− colorectal tumours and is essentially restricted to the MSI+ pathway (Guanti et al, 2000; Shin et al, 2001; Zhou et al, 2002).