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: However , there appeared to be a considerable variation in colchicine milk concentration among the different patients , which might be related to individual breast milk composition and , possibly , to other nutritional or metabolic factors .
### Output Text:
However , there appeared to be a considerable variation in colchicine milk concentration among the different patients , which might be related to individual breast milk composition and , possibly , to other nutritional or metabolic factors . 