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.
Finally, mitosis is how cells divide. Rapid growth in a tumor is generally an indication of a highly aggressive or very malignant process. Cells usually divide more frequently with more rapid growth, so a high mitotic rate can be an indication of a more malignant process. Grading combines an assessment of these three features, scored individually. A well-differentiated tumor is associated with a better prognosis than a poorly differentiated one.