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 age of cancer onset was not always distinct from typical sporadic cases .
### Output Text:
The age of <span class="disease">cancer</span> onset was not always distinct from typical sporadic cases . 