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: In this retrospective single - centre analysis , patients with relapsed or refractory HL treated with gemcitabine 1 , 000 mg / m ( 2 ) day ( D ) 1 , D8 and D15 ; methylprednisolone 1 , 000 mg D1 - 5 ; and cisplatin 100 mg / m ( 2 ) D15 , every 28 days ( GEM - P ) were included .
### Output Text:
In this retrospective single - centre analysis , patients with relapsed or refractory HL treated with <span class="chemical">gemcitabine</span> 1 , 000 mg / m ( 2 ) day ( D ) 1 , D8 and D15 ; <span class="chemical">methylprednisolone</span> 1 , 000 mg D1 - 5 ; and <span class="chemical">cisplatin</span> 100 mg / m ( 2 ) D15 , every 28 days ( <span class="chemical">GEM</span> - P ) were included . 