Neuroendocrine Tumors: Grades

Approved by the Cancer.Net Editorial Board, 04/2019

ON THIS PAGE: You will learn about how doctors describe how fast the tumor cells are growing and dividing, called the grade or degree of differentiation. Use the menu to see other pages.

Doctors may describe a NET by its World Health Organization (WHO) grade (G). Knowing the grade helps the doctor create a treatment plan for the NET. Grade and stage may be discussed at the same time when 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 NETs. The WHO grades for NETs include:

  • Grade 1 (low-grade tumor): These cells divide at a low rate and therefore grow slowly.

  • Grade 2 (intermediate-grade tumor): These cells divide at an intermediate rate.

  • Grade 3 (high-grade tumor): These cells divide at a fast rate and therefore grow quickly.

For many types of cancer, the grade also describes how much cancer cells look like healthy cells when viewed under a microscope, called degree of differentiation.

  • Well differentiated: The cells are well differentiated, which means they look more like healthy cells.

  • Poorly differentiated: The cells are poorly differentiated, which means they look less like healthy cells.

Mitosis is the process by which tumor cells grow and divide. Grading includes measurements of how fast mitosis is happening. To measure mitosis, the doctor counts the number of dividing cells seen in 10 high-power fields under a microscope. This is called the mitotic count. The doctor also measures the Ki-67 index. 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. 

The tumor’s grade and degree of differentiation may help the doctor predict how quickly the NET will grow and spread. In general, the lower the tumor’s grade and degree of differentiation, the better a person’s prognosis.

More detailed information about grading for a specific type of NET can be found in each specific NET section. See the Introduction for a list of those NETs.

Information about the tumor’s stage and grade will help the doctor recommend a specific treatment plan. The next section in this guide is Types of Treatment. Use the menu to choose a different section to read in this guide.