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: Univariate and adjusted analyses showed that the risk increased with the length of treatment ( p = 0 . 0001 ) or the cumulative dose of tamoxifen received ( p = 0 . 0001 ) , irrespective of the daily dose .
### Output Text:
Univariate and adjusted analyses showed that the risk increased with the length of treatment ( p = 0 . 0001 ) or the cumulative dose of <span class="chemical">tamoxifen</span> received ( p = 0 . 0001 ) , irrespective of the daily dose . 