What Are Grade, Stage, and Differentiation?
/GRADE
These tumors do not all behave or grow in the same way.
Grade refers to how fast or how slow the tumor is growing. Doctors use a sample of the tumor obtained through a biopsy or through surgery and examine it to determine how quickly the tumor cells are multiplying. The result is the Ki-67 index or the mitotic index, and the higher the measure, the higher the grade, on a range from Grade 1 or G1 (slower growing) to Grade 3 or G3 (faster growing).
Ki-67 is a protein in cells that is involved in cell replication, so if many cells are expressing it, the tumor is growing quickly. The pathologist needs to count about a thousand cells and determine the percentage of cells that are Ki-67 positive. The devil is in the details. Since it is not routine, it is often not done on specimens. Also, tiny little samples may not have enough cells to make it meaningful. And where was the sample taken from? We stained many tumors from several patients and found there is "heterogeneity" in the patients. In other words, one patient could have Ki67 of 1% in the primary tumor but 30% in a liver metastasis. Well, that certainly makes things more complicated. --Eric Liu, MD, FACS
STAGE
A tumor can start in one place and then spread (metastasize) to other parts of the body.
Stage refers to how advanced the cancer is--how far it has spread, or traveled, from where it began in the body. Using scans or imaging (CTs, MRIs, or various types of PET scans), doctors can “see” where the tumors are in your body. The stages range from Stage 1 (has not spread) to Stage 4 (spread to other organs or parts of the body).
DIFFERENTIATION
The structure of the cells that make up NET tumors is variable.
Differentiation refers to how the tumor cells look when compared to normal cells. Well-differentiated means the cells generally resemble normal cells, and these are usually slower growing tumors. Poorly-differentiated means the cell structures appear abnormally jumbled or disordered as compared to normal cells, and these are typically faster growing, more aggressive tumors. In lung NETs there are additional classifications: welldifferentiated lung NETs are further classified as typical or atypical, with the typical ones being more slow growing than the atypical ones. Atypical lung tumors are sometimes called moderately differentiated or poorly differentiated. Poorly differentiated lung neuroendocrine tumors may also be called large cell neuroendocrine tumors of the lung.
