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: After a period of 2 . 5 years on CPA treatment , four patients out of twenty - four were found to be affected by coronary heart disease .
### Output Text:
After a period of 2 . 5 years on <span class="chemical">CPA</span> treatment , four patients out of twenty - four were found to be affected by coronary heart disease . 