When grading a tumor, the pathologist is concerned with the microscopic appearance of the tumor cells, specifically with their degree of maturation or differentiation. Often, four grades are used. Grade I tumors are very well differentiated, so that they closely resemble the normal parent tissue of their origin. Grade IV tumors are so undifferentiated or anaplastic that even recognition of the tumor's tissue of origin may be difficult. Grade II and III are intermediate in appearance, moderately or poorly differentiated, as opposed to well differentiated that is grade I and undifferentiated grade IV.
Grading is often of value in the prognosis of certain types of cancers, such as cancer of the urinary bladder and ovary and brain tumors such as astrocytomas. Patients with grade I tumors have a high survival rate, and patients with grades II, III, and IV tumors have a poorer survival rate. Grading is also used in evaluating cells obtained from body fluids in preventive screening tests, such as Papanicolaou's or Pap smears of the uterine cervix, tracheal secretions, or stomach secretions.
The staging of cancerous tumors is based on the extent of spread of the tumor rather than on its microscopic appearance. An example of a staging system is the TNM staging system. It has been applied to malignancies such as lung cancer, as well as many other tumors. T refers to the size and degree of local extension of the tumor. N refers to the number of regional lymph nodes that have been invaded by tumor. M refers to the presence or absence of metastases that is spreads to distant sites of the tumor cells. Subscripts are used to denote size and degree of involvement. For instance 0 indicates undetectable and 1, 2, 3, and 4-a progressive increase in size or involvement. A tumor may be described as T1, N2, M0 that is a small tumor with spread to regional nodes, but no distant metastases.
TNM STAGING METHOD:
T0-No evidence of primary tumor
T IS-cancer in situ
T1, T2 T3 T4-Progressive increase in tumor size and involvement
TX-tumor cannot be assessed
N0-regional lymph nodes not demonstrably abnormal
N1, N2, N3, N4-increasing numbers or increasingly distant location of spread to regional lymph nodes.
Nx- regional lymph nodes cannot be assessed clinically.
M0- no evidence of metastasis.
M1, M2, M3, M4-Ascending degrees of distant metastasis
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