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 the current study the efficacy and toxicity of the combination of GEM and VNB in elderly patients with advanced NSCLC or those with some contraindication to receiving cisplatin were assessed .
### Output Text:
In the current study the efficacy and toxicity of the combination of <span class="chemical">GEM</span> and <span class="chemical">VNB</span> in elderly patients with advanced NSCLC or those with some contraindication to receiving <span class="chemical">cisplatin</span> were assessed . 