Grading of a neuroendocrine tumor describes how quickly the tumor may be growing and is used to develop a treatment plan. The grade can also help predict future outcomes (i.e., prognosis) and how the cancer might respond to treatment.  "Grade" and "stage" may be mentioned at the same time while NETs are being discussed, but they are very different elements in understanding the risk a tumor poses to a person. This section covers grading for neuroendocrine cancer.

 

Grade is determined by both the mitotic count and Ki-67 (also known as Antigen Kiel 67 or MKI67), which are both markers of how fast the tumor cells grow and divide. To determine the mitotic count, the number of dividing cells seen in a specific amount of space under a microscope (2 mm2) are counted.  The Ki-67 index is also measured. Ki-67 is a protein in cells that increases as they prepare to divide. If there is a high percentage of cells in an area with Ki-67, it means that the cells are dividing rapidly. The Ki-67 index is an indicator of how quickly the tumor cells are multiplying.  Factors used to determine the grade for NETs include:

• how often the cells of the tumor are dividing (measured as mitotic count and Ki-67 labelling index)

• the number of dead cells or tissues that are present (necrosis)

 

Grade classifications are defined by the World Health Organization (WHO) and are as follows:

• Low grade (grade 1, or G1) means that the cells of the tumor are slow growing.

• Intermediate grade (grade 2, or G2) means that the cells of the tumor are growing and dividing more quickly than normal cells.

• High grade (grade 3, or G3) means that the cells of the tumor are growing quickly. High-grade tumors are more likely to spread than low-grade and intermediate-grade tumors.