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: Bile duct hamartoma occurring in association with long - term treatment with danazol .
### Output Text:
Bile duct hamartoma occurring in association with long - term treatment with <span class="chemical">danazol</span> . 