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: Of the 82 evaluable patients , 50 did not show any recurrence after 1 year ( 61 % ) , while 32 presented with one or more recurrences ( 39 % ) .
### Output Text:
Of the 82 evaluable patients , 50 did not show any recurrence after 1 year ( 61 % ) , while 32 presented with one or more recurrences ( 39 % ) . 