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: A 47 - year - old woman presented for mastectomy and immediate latissimus dorsi flap reconstruction having been diagnosed with carcinoma of the breast 6 months previously .
### Output Text:
A 47 - year - old woman presented for mastectomy and immediate latissimus dorsi flap reconstruction having been diagnosed with carcinoma of the breast 6 months previously . 