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: Thirty - five consecutive chemotherapy - naive patients with Stage IV NSCLC and an Eastern Cooperative Oncology Group performance status of 0 - 2 were treated with a combination of paclitaxel ( 135 mg / m ( 2 ) given intravenously in 3 hours ) on Day 1 , cisplatin ( 120 mg / m ( 2 ) given intravenously in 6 hours ) on Day 1 , and gemcitabine ( 800 mg / m ( 2 ) given intravenously in 30 minutes ) on Days 1 and 8 , every 4 weeks .
### Output Text:
Thirty - five consecutive chemotherapy - naive patients with Stage IV NSCLC and an Eastern Cooperative Oncology Group performance status of 0 - 2 were treated with a combination of <span class="chemical">paclitaxel</span> ( 135 mg / m ( 2 ) given intravenously in 3 hours ) on Day 1 , <span class="chemical">cisplatin</span> ( 120 mg / m ( 2 ) given intravenously in 6 hours ) on Day 1 , and <span class="chemical">gemcitabine</span> ( 800 mg / m ( 2 ) given intravenously in 30 minutes ) on Days 1 and 8 , every 4 weeks . 