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: Echocardiographic data from the experimental group of 21 patients ( mean age 16 + / - 5 years ) treated from 1 . 6 to 14 . 3 years ( median 5 . 3 ) before this study with 27 to 532 mg / m2 of doxorubicin ( mean 196 ) were compared with echocardiographic data from 12 normal age - matched control subjects .
### Output Text:
Echocardiographic data from the experimental group of 21 patients ( mean age 16 + / - 5 years ) treated from 1 . 6 to 14 . 3 years ( median 5 . 3 ) before this study with 27 to 532 mg / m2 of <span class="chemical">doxorubicin</span> ( mean 196 ) were compared with echocardiographic data from 12 normal age - matched control subjects . 