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: Preliminary results of an Eastern Cooperative Oncology Group study of single - agent paclitaxel ( Taxol ; Bristol - Myers Squibb Company , Princeton , NJ ) reported a 37 % response rate in patients with head and neck cancer , and the paclitaxel / cisplatin combination has been used successfully and has significantly improved median response duration in ovarian cancer patients .
### Output Text:
Preliminary results of an Eastern Cooperative Oncology Group study of single - agent <span class="chemical">paclitaxel</span> ( <span class="chemical">Taxol</span> ; Bristol - Myers Squibb Company , Princeton , NJ ) reported a 37 % response rate in patients with head and neck cancer , and the <span class="chemical">paclitaxel</span> / <span class="chemical">cisplatin</span> combination has been used successfully and has significantly improved median response duration in ovarian cancer patients . 