A cancer occurs when a cell or cells abnormally divide when they should not. Cells are the body’s basic unit of life. Examples of cells in the body are red blood cells, muscle cells (sometimes called muscle fibers), and bone cells (osteocytes). Each type of cell can join or combine with another same type of cell to form a body tissue. For example, a muscle cell or cells combine to form a muscle tissue and nerve cells, called neurons, combine to form a nervous tissue.
Most of the cells of the body normally divide to form new cells to replace dead or worn-out cells. This dividing process that a certain cell undergoes is called cell division. Cell division is important for tissue repair, growth of an organ, and even the whole person. However, some cells are not able to divide and replace dead cells. For example, brain cells (neurons) are not able to divide and replace dead cells. This is the reason why as people grow older, brain functions are not as good as they used to be.
In cancer, however, cells divide when the body does not need them or they do not die when they’re supposed to. These abnormally dividing cells can form a mass referred to as a growth or tumor. The cancer cells may escape from the organ where they started and can cause cancer in other parts of the body by travelling through the circulatory system and/or the lymphatic system. This spreading of cancer is called metastasis.
A tumor may either be benign, meaning it is not cancerous or malignant, which is cancerous.
Benign tumors are not cancers. However, the abnormal cells continuously divide, thus, making the tumor grow larger and can be potentially dangerous if they compress other nearby organs. The cells from benign tumors do not travel or spread to other parts of the body, hence, they grow locally. Most benign tumors are rarely life threatening and usually can be removed. Also, this type of tumor, once removed, rarely grows back. Examples of benign tumors include hepatic adenoma, which is a benign tumor of the liver cells called hepatocytes and lipoma-a benign tumor that occurs in fat cells (lipocytes).
Malignant tumors are cancerous, often serious, and can be life threatening. They can be removed but can grow back. Cells from malignant tumors can escape from the organ where they started and can spread to other organs. Examples of malignant tumor or cancer include lung cancer and colorectal cancer.
There are more than a hundred types of cancer. Most of the common cancers are named according to the organ where they start. For example, a cancer that starts in the lining of or other parts the stomach is called stomach cancer or gastric cancer and colon cancer is the term used when cancer starts in any part of the colon. Sometimes, cancer is named according to the type of cell involved. Examples are basal cell carcinoma and leukemia. Basal cell carcinoma is a type of cancer that starts in the basal cells of the skin. Leukemia, on the other hand, involves blood cells called leukocytes. Leukocytes is the medical term for the white blood cells-the cells of the immune system.
Cancer is the most common cause of death worldwide, according to the World Health Organization (WHO). About 7.4 million deaths occurred worldwide due to cancer in 2004. Each year, the number of cancer related deaths are increasing. The World Health Organization estimates that in year 2030 there will be about 12 million deaths due to cancer.
US National Cancer Institute. Understanding Cancer Series: Cancer. National Institutes of Health (NIH). http://www.who.int/mediacentre/factsheets/fs297/en/index.html (Accessed on October 19, 2009)
US National Cancer Institute (May 11, 2009). What is Cancer? National Institutes of Health (NIH). http://www.cancer.gov/cancertopics/what-is-cancer (Accessed on October 20, 2009)
World Health Organization (WHO) Media Centre (Fact Sheet No. 297, February 2009).http://www.cancer.gov/cancertopics/understandingcancer/cancer/allpages/print (Accessed on October 20, 2009)
