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: Histological and immunohistochemical investigations ( HE - LFB , CD - 68 , Neurofilament ) revealed degeneration of myelin and axons as well as pseudocystic transformation in areas exposed to vincristine , accompanied by secondary changes with numerous prominent macrophages .
### Output Text:
Histological and immunohistochemical investigations ( HE - LFB , CD - 68 , Neurofilament ) revealed degeneration of myelin and axons as well as pseudocystic transformation in areas exposed to <span class="chemical">vincristine</span> , accompanied by secondary changes with numerous prominent macrophages . 