Grading describes what the cancer cells look like under a microscope. The grade gives an idea of how quickly the cancer may develop. The most common grading system for primary bone cancer uses two grades: low-grade and high-grade.
Low-grade means the cancer cells look very similar to normal bone cells. They are usually slow-growing and are less likely to spread.
In high-grade tumours, the cells look very abnormal. They are likely to grow more quickly and are more likely to spread. All Ewing’s sarcomas and most osteosarcomas and spindle cell tumours are high-grade.