How is cancer classified? Oncology terminology explained

According to CANSA, cancers may be classified by their primary site of origin or by their histological or tissue types.

Classification by primary site of origin

Cancers may be of a specific sort such as:

• Breast cancer
• Lung cancer
• Prostate cancer
• Liver cancer
• Prostate cancer
• Renal cell carcinoma (kidney cancer)
• Oral cancer
• Brain cancer

Classification by tissue type

According to CANSA, cancers are classified into six major categories based on tissue types:

• Carcinomas originate from the epithelial layer of cells that form the lining of external parts of your body or the internal linings of organs within your body
• Sarcomas originate in connective and supportive tissues including your muscles, bones, cartilage and fat. Bone cancer or osteosarcoma mostly affects young people
• Myelomas (a type of blood cancer) originate in the plasma cells of bone marrow that produce various antibodies in response to infections
• Leukaemia is a group of cancers that are classified as blood cancers. These cancers affect the bone marrow where blood cells are produced. When cancerous, the bone marrow begins to produce excessive immature white blood cells that fail to perform their usual actions and you're often prone to infection
• Lymphomas are cancers of the lymphatic system. Lymphomas may be of two types – Hodgkin's lymphoma and Non-Hodgkin's lymphomas. In Hodgkin's lymphoma there is characteristic presence of specific cells in the tissue samples which are not present in Non-Hodgkin's lymphoma
• Mixed types have two or more components of the cancer.

Classification by grade

Cancers can also be classified according to grade, which is determined by the abnormality of the cells when compared to surrounding normal tissues. As abnormality increases, so does the grade, from 1 to 4. Cells that are well-differentiated closely resemble normal specialised cells and belong to low grade tumours. Cells that are undifferentiated are highly abnormal when compared to surrounding tissues. These are high grade tumours.

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 tumour size (T), the degree of regional spread or node involvement (N), and distant metastasis (M) or spread. This is called the TNM staging.

Another simpler method of staging is where combinations are grouped into five less-detailed stages. Doctors classify four stages of cancer. These stages tell them how far the condition has spread:

• Stages 1 and 2 mean that your cancer is in an early phase. There's no spread and the cancer often responds well to treatment
• Stages 3 and 4 mean that the cancer cells have invaded surrounding tissue, or spread to different parts of your body. Stage 3 and 4 cancers are more complex to treat.

What is metastasis?

As cancer cells multiply, they invade and damage normal cells and can move to different parts of your body. Some cancers affect only a specific area, while other types spread to other areas of the body far from the place where they started. This process of spreading is called metastasis.

What are primary disease and secondary lesions?

The original cancer cells are called the primary disease. The cells that travel to other parts of your body and cause tumours there are called secondary lesions. These cancer cells travel through your blood or your lymphatic system to distant parts of your body where they form new tumours through metastasis. Another name for secondary lesions is metastatic disease. For example, when breast cancer spreads to your lungs it's still referred to as breast cancer because that's where it started. The lung cancer will be called 'secondary' to breast cancer.

What is 'prognosis'?

Prognosis is a measure of how likely you are to recover from cancer. It's your cancer specialist's opinion, based on his or her medical experience, the likely course of your cancer and your health – essentially a forecast of the likely outcome of your cancer. It does not take into account your unique, individual response to the disease and treatment.

What are 'remission' and 'survivorship'?

Remission can be partial or complete remission of one's cancer - and essentially means that the signs and symptoms of your cancer have reduced. Read more about remission here.

Over the years, oncologists started using a five-year timeframe to define survivorship: if your cancer didn't recur during the five years after either diagnosis or treatment, you were regarded as a 'survivor'. Regardless of your frame of reference, being a survivor is a unique experience for every cancer patient. Read more about the unique needs of cancer survivors here and here.