The pathologist can also identify other characteristics of the tumor cells, including tumor grade and the degree of cell differentiation. The term differentiated describes the extent to which cancer cells are similar in appearance and function to healthy cells of the same tissue type. The degree of differentiation often relates to the clinical behavior of the particular tumor. Grade is a classification system used by pathologists to describe the degree of differentiation of tumor cells. Conversely, the cells of Grade 3 or Grade 4 tumors are usually poorly differentiated or undifferentiated high-grade tumors, and are generally the most aggressive in behavior.
Some cancers also have special grading systems.
For example, pathologists use the Gleason system to describe the degree of differentiation of prostate cancer cells. The Gleason system uses scores ranging from Grade 2 to Grade 10. Lower Gleason scores describe well-differentiated, less aggressive tumors. Higher scores describe poorly-differentiated, more aggressive tumors. Patients should discuss questions about tumor grade and how it relates to their diagnosis and treatment with their doctor.