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: The 58 patients treated ( 41 men and 17 women ) had a median age of 59 years ( age range , 25 to 75 ) and a performance status of 0 through 2 .
### Output Text:
The 58 patients treated ( 41 men and 17 women ) had a median age of 59 years ( age range , 25 to 75 ) and a performance status of 0 through 2 . 