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 : We conclude that in transplants , there is a strong association between well - developed PTCR and TG , while the significance of mild PTCR and its predictive value in the absence of TG is unclear .
### Output Text:
CONCLUSIONS : We conclude that in transplants , there is a strong association between well - developed PTCR and TG , while the significance of mild PTCR and its predictive value in the absence of TG is unclear . 