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 authors describe the unusual association between diffuse B - cell gastric lymphoma and myotonic dystrophy , the most common form of adult muscular dystrophy , and sudden atrial fibrillation following one cycle of doxorubicin - based chemotherapy in the same patient .
### Output Text:
The authors describe the unusual association between diffuse B - cell gastric lymphoma and myotonic dystrophy , the most common form of adult muscular dystrophy , and sudden atrial fibrillation following one cycle of <span class="chemical">doxorubicin</span> - based chemotherapy in the same patient . 