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: Paclitaxel , cisplatin , and gemcitabine combination chemotherapy within a multidisciplinary therapeutic approach in metastatic nonsmall cell lung carcinoma .
### Output Text:
<span class="chemical">Paclitaxel</span> , <span class="chemical">cisplatin</span> , and <span class="chemical">gemcitabine</span> combination chemotherapy within a multidisciplinary therapeutic approach in metastatic nonsmall cell lung carcinoma . 