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: CONCLUSIONS : We have demonstrated an increased risk of VTE associated with the use of CPA / EE in women with acne , hirsutism or PCOS although residual confounding by indication cannot be excluded .
### Output Text:
CONCLUSIONS : We have demonstrated an increased risk of VTE associated with the use of <span class="chemical">CPA</span> / <span class="chemical">EE</span> in women with acne , hirsutism or PCOS although residual confounding by indication cannot be excluded . 