Grading describes how the cancer cells look compared to normal, healthy cells. Knowing the grade gives the healthcare team an idea of how quickly the cancer may be growing and how likely it is to spread.
To find out the grade of retinoblastoma, the pathologist looks at a tissue sample from the tumour under a microscope. They look at how different the cells look from normal cells (called differentiation) and other features of the tumour such as the size and shape of the cells and how the cells are arranged. They can usually tell how fast a tumour is growing by looking at how many cells are dividing.
The pathologist gives retinoblastoma a grade from 1 to 4. A lower number means the cancer is a lower grade.
Low-grade cancers have cancer cells that are well differentiated. The cells are abnormal but look a lot like normal cells and are arranged a lot like normal cells. Lower grade cancers tend to grow slowly and are less likely to spread.
High-grade cancers have cancer cells that are poorly differentiated or undifferentiated. The cells don’t look like normal cells and are arranged very differently. Higher grade cancers tend to grow more quickly and are more likely to spread than low-grade cancers.
Expert review and references
American Joint Committee on Cancer. AJCC Cancer Staging Handbook. 7th ed. Chicago: Springer; 2010.