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: METHODS : We reviewed the medical literature for single reports and case series of patients presenting with stroke - like episodes while receiving systemic or intrathecal chemotherapy .
### Output Text:
METHODS : We reviewed the medical literature for single reports and case series of patients presenting with stroke - like episodes while receiving systemic or intrathecal chemotherapy . 