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: At day 833 after the transplantation , he was diagnosed with PTLD ( post - transplantation lymphoproliferative disorder , Burkitt - type malignant lymphoma ) .
### Output Text:
At day 833 after the transplantation , he was diagnosed with PTLD ( post - transplantation lymphoproliferative disorder , Burkitt - type malignant lymphoma ) . 