The clinical impact of early detection of the YMDD mutant on the outcomes of long-term lamivudine therapy in patients with chronic hepatitis B.

The early emergence of lamivudine (3TC)-resistant tyrosine-methionine-aspartate-aspartate (YMDD) mutants has been reported during 3TC therapy in patients with chronic hepatitis B (CHB) in hepatitis B virus (HBV)-endemic areas; however, its clinical impact during long-term 3TC therapy is unknown. This study was performed to investigate the impact of the early emergence of YMDD mutants 3 months after the initiation of treatment on the outcomes of long-term 3TC therapy in HBV e antigen (HBeAg)-positive CHB. We analysed YMDD genotypes in consecutive samples from 30 patients with HBeAg positive CHB throughout 3TC treatment using both restriction fragment length polymorphism and mass spectrometric assays. Long-term outcome was compared between patients who had YMDD mutations detected at 3 months and those who had no mutations. YMDD mutation was detected in 16 (53.3%) out of 30 patients at 3 months and only the rtM2041 mutation was found. Cumulative HBeAg loss rates at 3 years was 12.5% and 57.4% in patients who had the rtM2041 mutant and wild-type virus at 3 months, respectively (P=0.010). Cumulative viral breakthrough rates at 3 years was 75.0% and 14.3% in patients who had the rtM204I mutant and wild-type virus at 3 months, respectively (P=0.002). Logistic regression revealed that YMDD mutation at 3 months was significantly related to viral breakthrough within 24 months (P=0.003). In conclusion, early detection for HBV YMDD mutation at 3 months may be useful to predict the long-term outcomes of 3TC therapy in patients with HBeAg-positive CHB in HBV-endemic areas.