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: RESULTS : A total of 76 cases of hyponatremia and / or SIADH associated with vincristine use were identified .
### Output Text:
RESULTS : A total of 76 cases of hyponatremia and / or SIADH associated with <span class="chemical">vincristine</span> use were identified . 