Abstract: Objective To explore gene mutations and mRNA expression of PTEN in cases of hepatocellular carcinoma （HCC） exvposed to both hepatitis B virus and aflatoxin B₁ （HBV/AFB₁）. Methods A total of 108 cases of HCC from different districts of Guangxi were divided into 4 groups according to their exposure to HBV and AFB₁：group A，HBV（+）/AFB₁-DNA（+），48 cases；group B，HBV （+）/AFB1-DNA（-），27 cases；group C，HBV（-）/AFB1-DNA（+），19 cases；and group D，HBV（-）/AFB₁-DNA（-），14 cases.PTEN mutations in exons 4，5，and 8 were detected by PCR and direct sequencing，and mRNA expression was analyzed by RT-PCR. Results PTEN mutations in exons 4，5，or 8 were not found in any of the cases. However，a large deletion at the junction of exon 4 and intron 4 was found in 61 cases，corresponding to a deletion rate of 56.4%.The rate of PTEN deletion was 60.4% in group A, 62.9% in group B，47.3% in group C and 46.6% in group D.The deletion rate was not statistically significant among the four sub-groups.Semi-quantitative gray values of the PTEN mRNA expression assay were as follows： group A，0.54 ± 0.13；group B，0.59± 0.16；group C，0.97 ± 0.16；group D，0.92 ± 0.13. The pair of groups A/B and the pair C/D differed significantly from each another in PTEN mRNA expression（P_AC=0.002，P_AD=0.032，P_BC=0.000，P_BD=0.011）. Conclusions Down-regulation of PTEN mRNA expression is a frequent molecular event in HCC involving double exposure to HBV/AFB₁ in Guangxi，and it may be related to HBV infection.AFB₁ and HBV may act synergistically to down-regulate PTEN mRNA levels.

Key words: Liver neoplasms, Hepatitis B virus, Aflatoxin B₁, PTEN