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: Our study suggests that prophylactic lamivudine significantly decreases the incidence of HBV reactivation and overall morbidity in cancer patients during and after immunosuppressive therapy .
### Output Text:
Our study suggests that prophylactic <span class="chemical">lamivudine</span> significantly decreases the incidence of HBV reactivation and overall morbidity in cancer patients during and after immunosuppressive therapy . 