Colorectal Cancer Chapter 4
What Is Colorectal Cancer?
The process of cell growth in the body is normally an orderly one. Cells grow and divide as necessary to produce more cells as they are needed. Cells that are old or damaged die, and are replaced with new cells.
In cancer, something has gone wrong with this process. The cell's DNA has been damaged. DNA is a substance found in every cell in the body that directs the cell's functioning and reproduction. Cell DNA may be damaged by environmental agents, such as radiation (including excessive sunlight), viruses, chemicals, and tobacco smoke. Cells with damaged DNA may also be inherited from one's parents.
Normally, if a cell has damaged DNA, it either repairs it or dies. But in cancer, the damaged cell starts to reproduce in an uncontrolled way, creating more abnormal cells. It outlives the normal cells around it and forms a tumor (a lump or mass).
Not all tumors are invasive. Benign tumors may simply be removed and are unlikely to grow back again. Malignant tumors, however, are cancerous, and they may start to invade surrounding tissues. By entering the bloodstream or the lymph system, cancer cells can spread throughout the body.
Types of Cancer
Cancer is not one disease. There are more than one hundred different types of cancer, and they all behave differently. Liver cancer, for instance, grows at a different rate than colorectal cancer, and responds to different treatments.
Cancer is named after the site where it originates, no matter where it spreads. Breast cancer that has spread to the lungs is termed metastatic breast cancer, not lung cancer.
Although there are many different types of cancer, they can all be divided into five main categories:
- Carcinoma. Cancer that begins in epithelial cells (cells that form the skin or tissues that line or cover internal organs)
- Sarcoma. Cancer that begins in connective tissue (such as bone, cartilage, fat, muscle, and blood vessels)
- Leukemia. Cancer that starts in blood-forming tissue (like bone marrow)
- Lymphoma and myeloma. Cancers that begin in the cells of the immune system
- Central nervous system cancers. Cancers that begin in the tissues of the brain or spinal cord
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