What is the difference between low-grade and high-grade uterine sarcoma?

When a biopsy or dilatation and curettage is done to take a tissue sample from the uterus, it is then analyzed under a microscope. If uterine sarcoma is present, it is classified as low-grade or high-grade. If few cancer cells are present, then it is called low-grade. If the tissue contains many cancer cells, it is called high-grade. High-grade sarcomas are considered more serious as they grow very quickly.