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: Increasing levels of serum bFGF and VEGF were associated with progressive disease ; five of six men who demonstrated a fall in PSA also showed a decline in bFGF and VEGF levels , and three of four men with a rising PSA showed an increase in both growth factors .
### Output Text:
Increasing levels of serum bFGF and VEGF were associated with progressive disease ; five of six men who demonstrated a fall in PSA also showed a decline in bFGF and VEGF levels , and three of four men with a rising PSA showed an increase in both growth factors . 