What is Cancer?
Cells within the body divide and multiply during their life cycle. This way, as older cells die, newer cells are able to take their place. The rate of growth and renewal of cells depends on the type and location of the cells within the body. For instance, the life span of a human adult's skin cells is around 50 days, and it takes about a month for new layers to move from the bottom layer of skin to the outer. The outer layer of skin that you are able to see contains the oldest skin cells. After these cells die, they are shed and the younger cells below take their place. The cells that make up the heart, however, grow at a much slower rate. In fact, fewer than 50% of heart cells die and are replaced during a person's lifespan.
Cancer, then, is a grouping of cells that are growing at an unnaturally high rate compared to surrounding cells. When newer cells multiply more quickly than older cells are dying, they begin to form a mass called a tumor. Not all tumors are cancerous, however. Tumors can be labeled using two terms:
- Malignant - characterized by rapid growth and a tendency to invade surrounding tissues
- Benign - does not show tendency of invading surrounding tissues and grows at a slower rate than malignant tumors
When malignant, or cancerous tumors, spread to surrounding tissues or muscles, it is known as metastasizing. When a tumor metastasizes, a secondary or further tumor is formed that is similar in qualities to the original tumor. For example, this means that if colon cancer metastasizes to an individual's liver, the new cancerous tumors are not liver cancer but metastatic colon cancer.
How is Cancer Classified?
Cancerous tumors are classified according to the type of cell the tumor originated from. These classification types include the following:
- Carcinoma - these types of cancers originate in cells that become tissues and muscles that line the surface of the body or body cavities. Skin, breast, and lung cancers are examples of specific diagnoses within this type.
- Sarcoma - these types of cancers originate in the cells that become connective tissues, bone, or cartilage. Osteosarcoma is a specific bone cancer and an example of a diagnosis within this category.
- Leukemia - these types of cancers originate in the bone marrow cells that develop into various components of blood and the circulatory system
- Lymphoma - these types of cancers originate in the bone marrow cells that develop into various components of the lymphatic system
- Germinoma - these types of cancers originate in the cells of germs within the body
- Blastoma - these types of cancers originate in what are known as blasts, cells which have not yet begun to differentiate into a specific type
Specific diagnoses of cancers are further named for their size and shape as well as their location within the body or which organ they affect.