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: Atrial fibrillation following chemotherapy for stage IIIE diffuse large B - cell gastric lymphoma in a patient with myotonic dystrophy ( Steinert ' s disease ) .
### Output Text:
Atrial fibrillation following chemotherapy for stage IIIE diffuse large B - cell gastric lymphoma in a patient with myotonic dystrophy ( Steinert ' s disease ) . 