Cancer

The oldest description of cancer were written in Egypt as early as 3000 BC as part of an ancient Egyptian textbook on surgery.

The word "cancer" comes from the Greek work carcinos, which means crab. Hippocrates used this term to describe the disease because the projections of a cancer invading nearby tissues. During the 16th century, when the theory of bodily humors prevailed, it was believed cancer was caused by excess black bile buildup; But this was discarded early when no black bile was found. After invention of the microscope, evidence accumulated that cancer was the result of uncontrolled cell division but the cause was still unknown.

Learning Objectives

1. Describe the distinguishing features of a cancer
2. Discuss the mechanism by which cancers evolve
3. Explain what is meant by "metastasis" and the mechanisms by which it occurs
4. Explain the difference between the "grade" and the "stage" of a cancer
5. Discuss risk factors for cancer and strategies for prevention
6. Define the following terms:
   • Cell differentiation
   • Benign tumor
   • Malignant tumor
   • Dysplasia
   • Carcinogen
   • Proto-oncogene and onogene
   • Tumor-suppessor gene (anti-oncogene)
   • Apoptosis

Cancer Biology

Cancer is the result of a long process that begins when one of the cells in organs or tissue becomes damaged or altered in a way that causes it to break free from normal controls that allow cells to work in harmony. Cancer cells with divide via mitosis even if they do not receive the appropriate signals. This can lead to a mass of cells, or a tumor.

The nucleus of a cell contains the genetic information, within the chromosomes. Certain genes make products that lead cells to reproduce. The genes responsible for making cells divide are called proto-oncogenes. Changes in normal genes lead to the production of proto-oncogenes, making cells divide faster. There are also genes that stop the division of cells, known as tumor-suppressor genes. We have two of these genes (one from each parent), so if one tumor-supporessor gene is damaged, usually the other is able to stop the cell from behaving abnormally.

The process by which tumors cause the body to provide the cell with nutrients is call angiogenesis. The tumor sends out messages that say "feed me" and the nearby blood vessels send over new extensions that deliver food and oxygen. The blood vessels also act as a passageway for movement of tumor cells. The movement of tumor cells to other parts of the body is called metastatis. 90% of cancer deaths occur when the tumor spreads to different parts of the body.

One way the development of cancer is prevented is the death of defective cells. If the body is unable to replace or repair the damaged cells it commits cellular suicide, or apoptosis.  This leads to the breakdown and death of the cell. Cancer cells lose this critical capability and lead to buildup of abnormal cells.

Cancer cells can also develop resistance to drug treatment in the same way bacteria might.