5.33 Grading and staging of tumor (1) Tumor Grade: The grading of a cancer attempts to establish some estimate of its aggressiveness or level of malignancy based on the differentiation of the tumor cells. Particular attention is given to the degree of cytologic atypia, including the number of mitoses within the tumor. Most tumors can be classified by the following general criteria: Grade Ⅰ: well differentiated, a tumor of low malignancy Grade Ⅱ: moderate differentiation, a tumor of moderate malignancy Grade Ⅲ: poor differentiation, a highly malignant tumor Grade IV: an anaplastic tumor. . The differentiation is often so poor that the cell type cannot be easily recognized by routine stains. These are usually the most highly malignant (aggressive) tumors.     Other grading systems: While these criteria can generally be used to grade most neoplasms, specific criteria are applied to grade some tumors. For example, grading of prostate cancer and lymphomas employs highly specific criteria and specialized grading systems. Decisions about therapy depend upon accurate grading and the use of these specialized grading systems.