The name, extent of differentiation or staging of cancer is useful in order to assess the patient’s overall condition, to develop a suitable treatment plan and predict possible treatment outcome.
Naming of Cancer
Cancer can be named based on the site where they originally started or the type of cells they are made up of. For example liver cancer started in the liver and it’s made up of liver cells. Whether this liver cancer spread to the lungs or not, it will still stay liver cancer. Another classification is based on the tissue structure the tumour is made up of and usually represents a more general description. Example can be seen below:
- Carcinoma is a cancer of the epithelial tissues (the tissues that line both the outer and internal surfaces of the body such as the skin or bladder)
- Sarcoma is a cancer of the connective tissues such as bones, muscle, cartilage and blood vessels
- Lymphoma is cancer of the lymphatic tissues
- Leukemia is cancer which developed from the bone marrow and produces useless white blood cells that cannot fight infection.
- Myeloma is cancer which affects specific white blood cells called plasma cells. These are cells which produce antibodies that are responsible for fighting a disease.
- Blastoma is cancer which develops from embryonic or developing tissues and is more common in children.
- There is no general description for cancer that affects the nervous tissues (tissues which make up the brain, spinal cord and nerves). However they are named according to the specific type of nervous tissue which is being affected. For example, a glioblastoma is cancer of the glial tissues.
Cancer can be classified based on how well it has differentiated or transformed. The more cancerous cells resemble the normal cells from which they originated, the more they are said to be differentiated. A poorly differentiated or anaplastic cancer is difficult to identify. If it cannot be identified easily, then the tissue from which it originated will be unknown and as such a treatment plan will be difficult to develop. Based on the extent of differentiation, cancer may be classified into four main grades.
- Grade I (well differentiated or low grade tumour): Very closely resembles the normal cells or tissues and easily diagnosed
- Grade II (Moderately differentiated or intermediate grade tumour): Resembles normal tissues only to an extent and diagnosis can either be good or poor.
- Grade III (Badly differentiated or high grade tumour): Very poorly differentiated from the normal tissues and look very abnomal
- Grade IV (Undifferentiated): Does not resemble the normal tissues from which it originated at all resulting to very poor diagnosis and treatment outcome.
The more badly differentiated a cancer cell is, the more abnormal it looks and the more it can easily migrate to other body parts.
While the grading system describes how abnormal a tumour is in appearance when compared to the normal cell, a staging system describes the size of the tumour and the extent to which it has spread to other body parts. Many staging system are in use and while some are used to describe specific types of cancer, others may be used to describe a broader range of cancer. The staging systems described below are only suitable for solid tumours. Blood cancers such as leukemia, lymphoma and myeloma have a different staging system.
Stage 0 to IV system
- Stage 0: It is also called the in situ stage and describes localized tumours that are not yet cancerous but have the potential to become cancerous. In order words they are precancerous.
- Stage II to III: It describes tumours that are now cancerous but have not grown beyond nearby tissues. The higher the number the larger the size of the tumour and the more deeply it has penetrated nearby tissues
- Stage IV: Also called the advanced stage describes a tumour that has spread to distant body parts or organs
The TNM staging system
This system is most widely used by clinicians and describes a tumour based on 3 criteria embedded in the acronym TNM. Here T stands for tumor, N for node and M for metastasis.
T: Describes the size and the extent of the primary tumour
- TX: Primary tumour cannot be measured
- T0: Primary tumour is absent
- T(is) or T in situ: The tumour is still localized
- T1, T2, T3 and T4: Describes the size and extent to which cancer has penetrated nearby tissues. The high the number the larger the size of the tumour and the deeper it has penetrated nearby tissues. T can be further divided into smaller sub-categories by adding lower case letters such as “a”, “b” or m. This subdivisions help to describe some cancer types by providing further details.
N: Describes if the cancer has spread to lymph nodes and if so how many lymph nodes have been affected.
- NX: Cancer in nearby lymph nodes cannot be measured
- N0: cancer is absent in nearby lymph nodes
- N1, N2, and N3: Describes the location or the number of lymph nodes affected. The greater N, the more lymph nodes are there that contains cancer.
M: Describes if the cancer cell has spread or metastasize to other body part.
- MX: Metastasis cannot be measured
- M0: The cancer has not spread or metastasize to other body parts or organs
- M1: Cancer has metastasize to other body parts
Other Staging Systems
Cancer cells may also be staged as in situ (describes presence of precancerous cells), localized (the cancer has not spread from its original site), regional (cancer is spread to nearby tissues or organs), distant (cancer has spread to distant body parts or organs) or unknown (the stage of the cancer cannot be determined due to limited information).