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: After adjusting for confounding factors , the risk was higher for tamoxifen users ( p = 0 . 0012 ) , treatment for more than 3 years ( all p < 0 . 03 ) and pelvic radiotherapy ( p = 0 . 012 ) .
### Output Text:
After adjusting for confounding factors , the risk was higher for <span class="chemical">tamoxifen</span> users ( p = 0 . 0012 ) , treatment for more than 3 years ( all p < 0 . 03 ) and pelvic radiotherapy ( p = 0 . 012 ) . 