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 HRAS1 variable number of tandem repeats ( VNTR ) polymorphism , located 1 kilobase ( kb ) downstream of the HRAS1 proto - oncogene ( chromosome 11p15 . 5 ) is one possible genetic modifier of cancer penetrance .
### Output Text:
The HRAS1 variable number of tandem repeats ( VNTR ) polymorphism , located 1 kilobase ( kb ) downstream of the HRAS1 proto - oncogene ( chromosome 11p15 . 5 ) is one possible genetic modifier of <span class="disease">cancer</span> penetrance . 