Structural Biochemistry/Classifications of Cancer
Cancers are classified in two ways: by the type of tissue in which the cancer originates (histological type) and by primary site, or the location in the body where the cancer first developed. This section introduces you to the first method: cancer classification based on histological type. The international standard for the classification and nomenclature of histologies is the International Classification of Diseases for Oncology, Third Edition (ICD-O-3).
Classification by tissue types
From a histological standpoint there are hundreds of different cancers, which are grouped into six major categories:
- Mixed Types (Blastoma)
Classification by site of origin
By primary site of origin, cancers may be of specific types like breast cancer, lung cancer, prostate cancer, liver cancer renal cell carcinoma (kidney cancer), oral cancer, brain cancer etc.
Classification by grade
Cancers can also be classified according to grade. The abnormality of the cells with respect to surrounding normal tissues determines the grade of the cancer. Increasing abnormality increases the grade, from 1–4.
Cells that are well differentiated closely resemble normal specialized cells and belong to low grade tumors. Cells that are undifferentiated are highly abnormal with respect to surrounding tissues. These are high grade tumors.
- Grade 1 – well differentiated cells with slight abnormality
- Grade 2 – cells are moderately differentiated and slightly more abnormal
- Grade 3 – cells are poorly differentiated and very abnormal
- Grade 4 – cells are immature and primitive and undifferentiated
Classification by stage
Cancers are also classified individually according to their stage. There are several types of staging methods. The most commonly used method uses classification in terms of tumor size (T), the degree of regional spread or node involvement (N), and distant metastasis (M). This is called the TNM staging.
For example, T0 signifies no evidence of tumor, T 1 to 4 signifies increasing tumor size and involvement and Tis signifies carcinoma in situ or limited to surface cells. Similarly N0 signifies no nodal involvement and N 1 to 4 signifies increasing degrees of lymph node involvement. Nx signifies that node involvement cannot be assessed. Metastasis is further classified into two – M0 signifies no evidence of distant spread while M1 signifies evidence of distant spread.
Stages may be divided according to the TNM staging classification. Stage 0 indicates cancer being in situ or limited to surface cells while stage I indicates cancer being limited to the tissue of origin. Stage II indicates limited local spread, Stage II indicates extensive local and regional spread while stage IV is advanced cancer with distant spread and metastasis.
- “Cancer Classification” By Dr Ananya Mandal, MD