1. Descriptive of something that distinguishes or separates one thing from another one: The differentiated markings on the wings of the brown butterfly identify it as a local insect, not a migratory one.
2. The similarity between a normal cell and the cancerous cell defines what degree of change has occurred: Cancerous cells that are well differentiated are close to the original cells and are usually less aggressive.

Poorly differentiated cells which have changed more and are more aggressive.