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: METHODS AND MATERIALS : Patients with ovarian or fallopian tube cancers or primary peritoneal carcinoma with platinum / paclitaxel - refractory disease ( stable or progressive disease following treatment with these agents or previous objective response < 3 months in duration ) were treated with liposomal doxorubicin at a dose of 40 mg / m ( 2 ) q 4 weeks .
### Output Text:
METHODS AND MATERIALS : Patients with ovarian or fallopian tube cancers or primary peritoneal carcinoma with <span class="chemical">platinum</span> / <span class="chemical">paclitaxel</span> - refractory disease ( stable or progressive disease following treatment with these agents or previous objective response < 3 months in duration ) were treated with liposomal <span class="chemical">doxorubicin</span> at a dose of 40 mg / m ( 2 ) q 4 weeks . 