Classification of cancer determines appropriate treatment and helps determine the prognosis. Cancer develops progressively from an alteration in a cell's genetic structure. This change (mutation) results in cells with uncontrolled growth patterns. Cancer classification is made according to the site of origin of the malignant cells; the histology, or cell analysis (called grading); and the extent of the disease (called staging).
Site of Cancer Origin
This classification describes the type of tissue in which the cancer cells begin to develop.
Here are some common examples of site of origin classification:
- Adenocarcinoma–originates in glandular tissue
- Blastoma–originates in embryonic tissue of organs
- Carcinoma–originates in epithelial tissue (i.e., tissue that lines organs and tubes)
- Leukemia–originates in tissues that form blood cells
- Lymphoma–originates in lymphatic tissue
- Myeloma–originates in bone marrow
- Sarcoma–originates in connective or supportive tissue (e.g., bone, cartilage, muscle)
Grading involves examining tumor cells that have been obtained through biopsy under a microscope. The abnormality of the cells determines the grade of the cancer. Increasing abnormality increases the grade, from 1–4. Cells that are well differentiated closely resemble mature, specialized cells. Cells that are undifferentiated are highly abnormal, that is, immature and primitive.
|Grade 1||Cells slightly abnormal and well differentiated|
|Grade 2||Cells more abnormal and moderately differentiated|
|Grade 3||Cells very abnormal and poorly differentiated|
|Grade 4||Cells immature and undifferentiated|
Staging is the classification of the extent of the disease. There are several types of staging methods. The tumor, node, metastases (TNM) system classifies cancer by tumor size (T), the degree of regional spread or node involvement (N), and distant metastasis (M).
|No evidence of tumor|
|Tis||Carcinoma in situ (limited to surface cells)|
|T1-4||Increasing tumor size and involvement|
|N0||No lymph node involvement|
|N1-4||Increasing degrees of lymph node involvement|
|Nx||Lymph node involvement cannot be assessed|
|M0||No evidence of distant metastases|
|M1||Evidence of distant metastases|
A numerical system also is used to classify the extent of disease.
|Stage 0||Cancer in situ (limited to surface cells)|
|Stage I||Cancer limited to the tissue of origin, evidence of tumor growth|
|Stage II||Limited local spread of cancerous cells|
|Stage III||Extensive local and regional spread|
|Stage IV||Distant metastasis|