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: Long - term follow - up of ifosfamide renal toxicity in children treated for malignant mesenchymal tumors : an International Society of Pediatric Oncology report .
### Output Text:
Long - term follow - up of <span class="chemical">ifosfamide</span> renal toxicity in children treated for malignant mesenchymal tumors : an International Society of Pediatric Oncology report . 