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: Twenty carcinomas of the urinary bladder and one carcinoma of the prostate have been reported in association with its use .
### Output Text:
Twenty carcinomas of the urinary bladder and one carcinoma of the prostate have been reported in association with its use . 