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: Most multiple case families of young onset breast cancer and ovarian cancer are thought to be due to highly penetrant mutations in the predisposing genes BRCA1 and BRCA2 .
### Output Text:
Most multiple case families of young onset <span class="disease">breast cancer</span> and <span class="disease">ovarian cancer</span> are thought to be due to highly penetrant mutations in the predisposing genes BRCA1 and BRCA2 . 