In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Sustained clinical improvement of a patient with decompensated hepatitis B virus - related cirrhosis after treatment with lamivudine monotherapy .
### Output Text:
Sustained clinical improvement of a patient with decompensated hepatitis B virus - related cirrhosis after treatment with <span class="chemical">lamivudine</span> monotherapy . 