This will be a multi-center study in Hong Kong. This is a retrospective-prospective study in HBeAg-negative chronic hepatitis B patients. HBeAg-negative patients on entecavir followed up in the liver clinics will be identified from the existing database. All patients had HBV DNA testing every 6 months as a clinic routine. Serum HBsAg levels will be tested in the residual serum samples at the pre-treatment and last follow-up visits. Eligible patients will be discussed on the plan of stopping entecavir therapy. All patients will have written informed consent before recruited into this study. All patients will be followed up for 12 months after stopping entecavir treatment. As entecavir is most commonly used antiviral drug in Hong Kong and in the Western countries, the investigators aim to investigate and validate the use of serum HBsAg quantification to guide the timing of stopping entecavir in HBeAg-negative patients. The results of this study will provide scientific evidence on the use of this new serum marker to predict sustained remission after stopping entecavir. In the long-run, it can improve patient compliance, reduce the need of long-term antiviral and reduce the drug cost in the management of HBeAg-negative chronic hepatitis B.

All patients will stop entecavir according to the Asian Pacific guideline with written informed consent and close subsequent monitoring. In the protocol, there is a safety net for re-treatment. There will not be any invasive procedure. There is no major ethical issue.

Chronic hepatitis B is the commonest cause of liver cirrhosis and hepatocellular carcinoma in Hong Kong. Approximately 50% of patients had negative hepatitis B e antigen (HBeAg), which indicates an escape of host immune clearance by the host. Oral antiviral drugs are very effective in suppressing viral replication and inducing biochemical remission [1]. However, the timing to stop oral antiviral agents is controversial. Hepatitis B surface antigen (HBsAg) seroclearance has been recommended as the best time for drug cessation for HBeAg-negative patients [2,3], but its occurrence is very uncommon especially among Asian patients. The Asian Pacific guideline recommended stopping treatment when serum HBV DNA became undetectable for three times within 12 months [4], but approximately 50% of patients will experience virologic relapse post-treatment [5,6].

HBsAg quantification has been shown to correlate with the concentration of covalently closed circular DNA in the liver [7]. In a Hong Kong study among 53 HBeAg-negative patients who stopped lamivudine, HBsAg ≤ 100 IU/ml and/or reduction of > 1 log at the end of treatment could predict sustained response up to 5 years post-treatment [8]. In other words, it is probable that patients who have a lower serum HBsAg level, which may reflect a lower concentration of virus inside the liver, have a lower risk of viral relapse after stopping antiviral therapy.

Inclusion Criteria:

1. HBeAg-negative patients on entecavir monotherapy for at least 24 months
2. Undetectable HBV DNA by PCR-based assay on 3 separate occasions 6 months apart (as per Asian Pacific guideline in 2008).
3. Normal ALT levels according to the local laboratory reference value on 2 separate occasions 6 months apart

Exclusion Criteria:

1. Patients previously or currently on interferon therapy
2. Patients who have experienced another antiviral agent besides entecavir
3. Patients with hepatitis C virus infection as indicated by a positive anti-HCV serology test
4. Patients with Child's B liver cirrhosis, cirrhotic complications or hepatocellular carcinoma
5. Patients with organ transplantation
6. Serious medical illnesses or malignancy
7. Age < 18 years or > 65 years
8. No patient consent

HBeAg-negative patients on entecavir followed up in the liver clinics will be identified from the existing database. All patients had HBV DNA testing every 6 months as a clinic routine. Serum HBsAg levels will be tested in the residual serum samples at the pre-treatment and last follow-up visits. Eligible patients will be discussed on the plan of stopping entecavir therapy. All patients will have written informed consent before recruited into this study. All patients will be followed up for 12 months after stopping entecavir treatment.