Cancer Classification and Metastasis
Cancer is a group of diseases in which abnormal cells grow and divide uncontrollably, destroying body tissue.
Cancers are classified according to the type of tissue in which the cancer originates and by the primary location where the cancer first developed. Based on tissue type, cancers are classified into six major categories:
- Carcinoma is a malignant tumor of epithelial cells, which are found in skin and the covering and lining of organs and internal passageways, such as the GI tract. Carcinomas usually affect organs capable of secretion including breast, lung, bladder, prostate, and colon. There are two types of carcinomas: adenocarcinoma and squamous cell carcinoma. Adenocarcinoma develops in mucus-secreting glands and is rapidly spreading. Squamous cell carcinoma is one of the main types of skin cancer.
- Sarcoma is a malignant tumor of connective and supportive tissue cells, including muscles, tendons, fat, cartilage, blood & lymph vessels, nerves, and tissue around joints. Sarcoma can also originate in the bone. Soft tissue and bone sarcomas are the main types of sarcomas.
- Myeloma is a cancer originating in the plasma cells of bone marrow. Plasma cells are white blood cells that produce antibodies. When myeloma cells prevent the normal production of antibodies, the immune system is weakened and there is an interference with the normal production and function of red and white blood cells. Patients often have bone pain or fractures, anemia, and susceptibility to infection. A single cell plasma cell tumor is called an isolated (or solitary) plasmacytoma, and more than one plasmacytoma is called multiple myeloma.
- Leukemia is cancer of the blood involving the bone marrow and lymph nodes. When cancerous, the bone marrow produces abnormal white blood cells that fail to provide immunity, causing the patient to be prone to infection. Leukemia also affects red blood cells and can cause poor blood clotting and fatigue from anemia.
- Lymphoma is cancer of the lymphatic system and develops in the glands or lymph nodes. There are two types: Hodgkin’s lymphoma and non-Hodgkin’s lymphoma. The cancerous cells of Hodgkin’s lymphoma crowd out normal white cells, and the immune system is unable to effectively guard against infection. The difference between the two types of lymphomas is determined during a biopsy of a lymph node; the presence of Reed-Sternberg cells (huge mutated B lymphocytes) distinguishes Hodgkin’s lymphoma from non-Hodgkin’s lymphoma.
- Mixed types have two or more components of cancer, such as carcinosarcoma or teratocarcinoma.
Whereas medical professionals refer to cancers based on their tissue type, the general public is more familiar with cancer names based on their primary body sites.
The most common sites in which cancer develops include:
- female breasts
Cancer names based on their primary site are often not as accurate as those based on tissue type. However, cancer can be classified by either the tissue cell type or its primary site. For example, uterine cancer is the same as carcinoma of the uterus.
Cancers can also be classified by grade, in which the cancer is examined for its cellular maturity and characteristics. Cells that are undifferentiated are highly abnormal, or immature and primitive, with respect to surrounding tissues.
- Grade 0 – Normal tissue
- Grade 1 – Well differentiated cells with slight abnormality
- Grade 2 – Moderately differentiated cells that have more abnormalities
- Grade 3 – Poorly differentiated cells that are very abnormal
- Grade 4 – Very undifferentiated and immature cells, meaning there is no resemblance to the tissue of origin
Cancers are also classified according to their stage. The most commonly used method is called the TNM staging. “T” stands for tumor size, “N” is the degree of regional spread or node involvement, and “M” stands for distant metastasis.
T0 represents no evidence of tumor, T1 to T4 represents increasing tumor size and involvement, and Tis represents carcinoma in situ (or abnormal cells that remain in the place where they first formed).
N0 represents no nodal involvement and N1 to N4 signifies increasing degrees of lymph node involvement. Nx indicates that node involvement cannot be assessed.
M0 represents no evidence of distant metastasis and M1 represents evidence of metastatic involvement.
For many cancers, the TNM combinations are grouped into five less-detailed stages:
- Stage 0 – Also called carcinoma in situ, abnormal cells are present but have not spread to nearby tissue.
- Stage 1, 2, and 3 – Cancer is present; the higher the number, the larger the tumor and the more it has spread into nearby tissues.
- Stage 4 – The cancer has spread to distant parts of the body.
Cancer cells do not serve any useful function, and they can migrate through blood vessels and tissues, spreading and growing in other body locations. This process is called metastasis and is the major cause of cancer death.
Cancer can spread by moving into or invading nearby normal tissue. The cancer cells break away from where they first formed (primary cancer), move through the blood vessels or lymph nodes, traveling to other parts of the body. At a distant location the cancer cells again go through the vessel walls, moving into the surrounding tissue and forming a new tumor (metastatic tumor). Metastatic cancer cells have features like that of the primary cancer, and therefore have the same name as the primary cancer. For example, breast cancer that spreads to the brain is called metastatic breast cancer, not brain cancer.
Cancer can spread to any part of the body, but different types of cancer are more likely to spread to certain areas than others. The most common sites where cancer spreads include bone, liver, and lung.
Some common sites of metastasis include the following:
- Breast cancer metastasizes to bone, brain, liver, & lung.
- Colon, ovary, pancreas, rectal, and stomach cancer metastasize to liver, lung, and peritoneum.
- Bladder cancer goes to bone, liver, and lung.
- Kidney cancer can move to adrenal gland, bone, brain, liver, or lung.
- Lung cancer goes to adrenal gland, bone, brain, liver, or other lung.
- Melanoma can go to bone, brain, liver, lung, skin, or muscle.
- Prostate cancer metastasizes to adrenal gland, bone, liver, and lung.
- Thyroid cancer to bone, liver, or lung.
- Uterine cancer can move to vagina, bone, liver, lung, or peritoneum.
Once cancer spreads, it can be hard to control. Most types of metastatic cancer cannot be cured with current treatment, but there are treatments with the goal of stopping or slowing the growth of the cancer or relieving symptoms to help prolong life. If the metastatic cancer can no longer be controlled, end-of-life care needs to be discussed.
Thank you for watching this video on the classification and metastasis of cancer.