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: OBJECTIVES : To assess the effect of long - term HT on mortality , heart disease , venous thromboembolism , stroke , transient ischaemic attacks , breast cancer , colorectal cancer , ovarian cancer , endometrial cancer , gallbladder disease , cognitive function , dementia , fractures and quality of life .
### Output Text:
OBJECTIVES : To assess the effect of long - term HT on mortality , heart disease , venous thromboembolism , stroke , transient ischaemic attacks , breast cancer , colorectal cancer , ovarian cancer , endometrial cancer , gallbladder disease , cognitive function , dementia , fractures and quality of life . 