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: We have analyzed the 27 exons and the promoter region of the RB1 gene in familial or sporadic bilateral retinoblastoma by using single - strand conformation polymorphism analysis .
### Output Text:
We have analyzed the 27 exons and the promoter region of the RB1 gene in <span class="disease">familial or sporadic bilateral retinoblastoma</span> by using single - strand conformation polymorphism analysis . 