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: Salvage therapy with nelarabine , etoposide , and cyclophosphamide in relapsed / refractory paediatric T - cell lymphoblastic leukaemia and lymphoma .
### Output Text:
Salvage therapy with <span class="chemical">nelarabine</span> , <span class="chemical">etoposide</span> , and <span class="chemical">cyclophosphamide</span> in relapsed / refractory paediatric T - cell lymphoblastic leukaemia and lymphoma . 