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: CONCLUSIONS The DPC4 gene may play a role as a tumor - suppressor gene in a fraction of colorectal cancers ; however , while allelic loss at 18q21 is very often seen in colorectal cancers , only a minority show DPC4 mutations , suggesting that there might be another tumor - suppressor gene in this chromosome region . .
### Output Text:
CONCLUSIONS The DPC4 gene may play a role as a tumor - suppressor gene in a fraction of <span class="disease">colorectal cancers</span> ; however , while allelic loss at 18q21 is very often seen in <span class="disease">colorectal cancers</span> , only a minority show DPC4 mutations , suggesting that there might be another tumor - suppressor gene in this chromosome region . . 