A well-differentiated tumor histologically looks a lot like the type of tissue from which it was derived, and is easily recognizable as such. A poorly differentiated carcinoma looks very little like its tissue of origin.
Improved prognosis correlates with better differentiation.
Numerous grading schemes have been proposed, but the one most widely recognized is that revised by Elston, and is often referred to as the Elston and Ellis, or combined, histologic grade. It is called the combined histologic grade because three histologic factors are evaluated to come up with a final tumor grade. Tubule formation is an assessment of the formation of gland-like spaces by tumor cells. Well-differentiated tumors have the most tubule formation, and poorly differentiated tumors have the least. Pleomorphism refers to the amount of variability, or atypia, of tumor cell nuclei.