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: RESULTS : RIHA , defined as a reduction in hemoglobin to less than 100 g / L , occurs in approximately 7 % to 9 % of patients treated with combination therapy .
### Output Text:
RESULTS : RIHA , defined as a reduction in hemoglobin to less than 100 g / L , occurs in approximately 7 % to 9 % of patients treated with combination therapy . 