Material submitted for tissue examination may be classified according to its histologic or cellular characteristics. The grade of the tumor is determined according to the histologic or cellular characteristics. Grading systems may differ based on the type of cancer that is identified; the lower the grade, the closer to normal the cells appear. Overall, if a specific grading system is not specified, tumors are graded as:
Grade X (GX): Undetermined grade.
Grade 1 (G1) (low grade): Tumor is well differentiated.
Grade 2 (G2) (intermediate grade): Tumor is moderately differentiated.
Grade 3 (G3) (high grade): Tumor is poorly differentiated.
Grade 4 (G4) (high grade): Tumor is undifferentiated.
The tumor–node–metastasis (TNM) staging system is a method of identifying tumor stage according to spread (or extent) of the disease. This system evolved from the work of the International Union Against Cancer and the American Joint Committee on Cancer. In addition, the TNM staging system further defines each specific type of cancer (e.g., breast, head, neck). This staging system is used for previously untreated and treated cancers and classifies the primary site of cancer and its extent and involvement, such as lymphatic and venous invasion.