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: The incidence of non - hematological toxicities was low and grade 3 - 4 hematological toxicities were reported in 20 patients ( mainly lymphopenia and neutropenia ) .
### Output Text:
The incidence of non - hematological toxicities was low and grade 3 - 4 hematological toxicities were reported in 20 patients ( mainly lymphopenia and neutropenia ) . 