What exactly does grade 1, 2, 3, 4 of the tumor mean in clear cell renal cell carcinoma?

How cells look. Grading refers to how closely the cancer cells resemble normal kidney cells. Cells that are more abnormal (ie higher grade) are associated with a worse prognosis.
Cell size and shape. When a clear cell renal cell carcinoma is removed, the cells are examined under the microscope by a pathologist. Grade 1 means that the nuclei (which contain cells' dna) are very small and often correlates with a good prognosis. Grade 4 means that the nuclei are very large and abnormal and often suggests a worse prognosis. Grades 2-3 are in between. Grade 2 is probably the most common.