In the sentence extracted from biomedical literature, identify all the disease entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="disease"> to denote a disease.

### Input Text: The von Hippel - Lindau tumor suppressor gene product interacts with Sp1 to repress vascular endothelial growth factor promoter activity .
### Output Text:
The <span class="disease">von Hippel - Lindau tumor</span> suppressor gene product interacts with Sp1 to repress vascular endothelial growth factor promoter activity . 