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: Preliminary results indicate that testosterone - treated LW rats that were fed the same diet , which was supplemented with corn oil up to 20 % fat , developed prostate cancer after intervals of 6 - 12 months .
### Output Text:
Preliminary results indicate that <span class="chemical">testosterone</span> - treated LW rats that were fed the same diet , which was supplemented with corn oil up to 20 % fat , developed prostate cancer after intervals of 6 - 12 months . 