In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: CONCLUSIONS : Familial thyroid illness is a risk factor for hypothyroidism and hypercalcemia during lithium therapy .
### Output Text:
CONCLUSIONS : Familial thyroid illness is a risk factor for hypothyroidism and hypercalcemia during <span class="chemical">lithium</span> therapy . 