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: CONCLUSION : The MTD of cis - RA given on this intermittent schedule was 160 mg / m2 / d .
### Output Text:
CONCLUSION : The MTD of <span class="chemical">cis - RA</span> given on this intermittent schedule was 160 mg / m2 / d . 