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: The patients , a 43 - year - old man , presented all the signs and symptoms of APL and was included in a treatment protocol with ATRA .
### Output Text:
The patients , a 43 - year - old man , presented all the signs and symptoms of APL and was included in a treatment protocol with <span class="chemical">ATRA</span> . 