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: The results obtained indicate that with all three carcinogens , administration of 5 - AzC during repair synthesis increased the incidence of initiated hepatocytes , for example 10 - 20 foci / cm2 in 5 - AzC and carcinogen - treated rats compared with 3 - 5 foci / cm2 in rats treated with carcinogen only .
### Output Text:
The results obtained indicate that with all three carcinogens , administration of <span class="chemical">5 - AzC</span> during repair synthesis increased the incidence of initiated hepatocytes , for example 10 - 20 foci / cm2 in <span class="chemical">5 - AzC</span> and carcinogen - treated rats compared with 3 - 5 foci / cm2 in rats treated with carcinogen only . 