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: She had ovarian failure after abdominal irradiation and chemotherapy for Hodgkin disease , and received exogenous estrogens , a treatment implicated in the development of endometrial cancer in menopausal women .
### Output Text:
She had ovarian failure after abdominal irradiation and chemotherapy for Hodgkin disease , and received exogenous <span class="chemical">estrogens</span> , a treatment implicated in the development of endometrial cancer in menopausal women . 