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 two genes are believed to interact in a number of pathways , including regulation of DNA damage - induced cell - cycle checkpoints , apoptosis and radiation sensitivity , and cellular proliferation .
### Output Text:
The two genes are believed to interact in a number of pathways , including regulation of DNA damage - induced cell - cycle checkpoints , apoptosis and radiation sensitivity , and cellular proliferation . 