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: Intracavitary chemotherapy in recurrent glioblastoma using cubic phases is feasible and safe , yet the clinical benefit remains to be examined in a clinical phase II study .
### Output Text:
Intracavitary chemotherapy in recurrent glioblastoma using cubic phases is feasible and safe , yet the clinical benefit remains to be examined in a clinical phase II study . 