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: Mice doubly null for atm and p53 exhibited a dramatic acceleration of tumour formation relative to singly null mice , indicating that both genes collaborate in a significant manner to prevent tumorigenesis .
### Output Text:
Mice doubly null for atm and p53 exhibited a dramatic acceleration of <span class="disease">tumour</span> formation relative to singly null mice , indicating that both genes collaborate in a significant manner to prevent tumorigenesis . 