Patients with Stage 4 brain cancer have cancer that has grown and metastasized (or spread) to the nearby tissues. Tumor cells actively divide and appear very different from the normal cells. It is found that the tumors in the brain very rarely metastasize to other parts of the body, but there are greater chances that these tumors may grow and affect other parts of the central nervous system. Researchers suggest that grading brain cancer is different from other cancer as tumors in the brain are graded based on how aggressive the tumor cells appear under a microscope.