Most cancers in people are staged to determine the extent and prognosis and to select the treatment options. Staging is a standard means for healthcare professionals to summarize information about the cancer. Brain tumors differ from tumors in other parts of the body. With other tumors, one of the most deadly aspects of the cancer is the extent to which it has spread in the body. Primary brain tumors rarely spread to other organs. For this reason, brain tumors are not staged. Instead, tumor grading is used to facilitate communication, plan treatment and predict the outcome for recovery.

The World Health Organization (WHO) has established a grading system for tumors that is based microscopic examination of tissue using the following criteria:

• Differences from normal cells (atypia)
• Rate of growth (mitotic index)
• Indications of uncontrolled growth
• Dead tumor cells in the center (necrosis)
• Potential for invasion or spreading (infiltration)
• Margin of the tumor (diffuse or focal)
• Blood supply (vascularity)

This WHO grading system may be used for adult brain tumors:

• Grade I
  
  
• Slow-growing cells
• Almost normal appearance under a microscope
• Least malignant
• Rarely spreads into nearby tissue
• May be possible to remove entire tumor by surgery
• Usually associated with long-term survival
  
  
• Grade II
  
  
• Relatively slow-growing cells
• Slightly abnormal appearance under a microscope
• Can invade nearby tissue
• Can become a higher-grade tumor
  
  
• Grade III
  
  
• Actively growing abnormal cells
• Abnormal appearance under a microscope
• Grows very quickly
• Likely to spread to nearby tissue
• Tends to recur as a higher-grade tumor
  
  
• Grade IV
  
  
• Abnormal cells that reproduce rapidly
• Very abnormal appearance under the microscope
• Forms blood vessels that maintain rapid growth
• Areas of dead cells in center
• Difficult to treat successfully

Tumors often contain several grades of cells. The highest or most malignant grade of cell determines the grade of the tumor, even if most of the tumor is lower grade. Some tumors may change, such as a benign tumor may become malignant. In some cases, a lower-grade tumor may recur as a higher grade.

The choice of treatment and chance of recovery are dependent on the type, location, and grade of the tumor. Whether cancer cells remain in the brain and whether they have spread to other parts of the brain will also affect a patient’s prognosis.