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 Rb1 gene has been implicated with retinoblastoma and is located on human Chromosome ( Chr ) 13q14 .
### Output Text:
The Rb1 gene has been implicated with <span class="disease">retinoblastoma</span> and is located on human Chromosome ( Chr ) 13q14 . 