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: To begin to address the hypothesis that abnormal regulation of the breast / ovarian cancer susceptibility gene BRCA1 is a critical step in sporadic breast / ovarian tumorigenesis , we have determined the detailed structure of the BRCA1 genomic region .
### Output Text:
To begin to address the hypothesis that abnormal regulation of the <span class="disease">breast / ovarian cancer</span> susceptibility gene BRCA1 is a critical step in sporadic breast / ovarian tumorigenesis , we have determined the detailed structure of the BRCA1 genomic region . 