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: Her aspartate transaminase and alanine transaminase levels increase markedly after 6 months of tamoxifen use .
### Output Text:
Her <span class="chemical">aspartate</span> transaminase and <span class="chemical">alanine</span> transaminase levels increase markedly after 6 months of <span class="chemical">tamoxifen</span> use . 