Summary Cigarette smoking has been associated with increased risk of hepatocellular carcinoma (HCC) in some epidemiological studies. Cytochrome P450 1A1 (CYP1A1) is involved in the biotransformation of tobacco-derived polycyclic aromatic hydrocarbons (PAHs) into carcinogenic metabolites. The aim of this study was to determine whether CYP1A1 polymorphisms were related to HCC risk among chronic hepatitis B virus (HBV) carriers. Genotypic variants of CYP1A1 were determined using polymerase chain reaction in 81 incident cases of HCC and 409 controls nested in a cohort study of 4841 male chronic HBV carriers. No overall association between CYP1A1 genotypes and HCC was observed. The presence of the MspI (odds ratio (OR) 3.15, P = 0.0196) or Ile-Val (OR 1.99, P = 0.0855) variant allele of CYP1A1 increased HCC risk among smokers, but posed no increased risk among non-smokers. The smoking-related HCC risk was most pronounced among those who had a susceptible allele of the CYP1A1 and a deficient genotype of glutathione S-transferase M1, which detoxifies PAH electrophilic metabolites produced by CYP1A1. In the absence of the Ile-Val variant allele, the MspI polymorphism was still associated with smoking-related HCC. This study suggests that tobacco-derived PAHs play a role in HCC risk among chronic HBV carriers, and CYP1A1 polymorphism is an important modulator of the hepatocarcinogenic effect of PAHs. The MspI and Ile-Val polymorphisms of CYP1A1 may have different mechanisms for increasing susceptibility to smoking-related HCC.

Twenty-five years after its first description the p53 protein has been shown to play a key role in both cancer and ageing. The p53 protein is activated by many different stress pathways, including oncogene action and DNA damage. The elucidation of the p53 response, which is aberrant in most cancers (including breast, lung, stomach and colorectal cancer), has provided many new targets for drug development and p53 gene therapy is now approved in China. In tumours where p53 is mutant small molecules may be able to restore its function. In many tumours the wild-type p53 gene remains intact but its function is compromised by loss of upstream signalling pathways or downstream effectors. A key regulator is Mdm2, an E3 ubiquitin ligase, that binds and ubiquitinates p53 and directs its degradation via the proteosome. Small potent peptides that can block the p53 Mdm2 interaction and activate the p53 response have been described. Growing selections of lead small molecules that mimic the action of these peptides have also been recently discovered. Cell-based screens have revealed that inhibitors of nuclear export and inhibitors of transcription (one of which is in clinical trial) can also activate the p53 response therapeutically. The pharmaceutical regulation of the p53 pathway offers great hope for improved treatment of human cancer.