The oldest descriptions of cancer were written in Egypt as early as 3000 B.C., as part of an ancient Egyptian textbook on surgery. The name, "cancer" comes from the Greek word carcinos, which means crab. Hippocrates used this term to describe the disease because of the projections of a cancer invading nearby tissues. During the 16th century, when the theory of bodily humors prevailed, it was believed that an excess of black bile caused cancer. The renowned anatomist Andreas Vesalius searched diligently for this black bile and ultimately discarded the this theory when he was unable to find it. In 1838 a botanist named Matthias Schleiden and Theodor Schwann, a physiologist, proposed that all living things were composed of fundamental units called cells. Shortly after the introduction of this idea, Virchow (the "father" of pathology) proposed that cells only arose from other cells and that growth could only occur as a result of hypertrophy or hyperplasia. Virchow studied cancers under with a microscope and recognized that they represented hyperplasia in an extreme form that he dubbed "neoplasia."
Evidence accumulated to support the idea that cancer was the result of uncontrolled cell division, but the cause was unknown. The earliest clues came from epidemiologic observations. For example, in 1775 Dr. Percival Pott, an English surgeon, reported on the unusual occurrence of scrotal cancer in men who had worker as chimney sweeps as boys, and he speculated that the soot, tars, and dirt to which the chimney sweeps were chronically exposed may have played a role. Another Englishman, John Hill, warned that excessive use of snuff or chewing tobacco might lead to nasal cancer or cancers of the mouth, tongue, or lip. Nevertheless, it wasn't until the last three decades of the the 20th century that the biological origins of cancers began to be revealed. This module will provide our current understanding of the biological basis of cancer, determinants of the disease, and ways to prevent or reduce the risk of getting cancer.
After successfully completing this module, you will be able to:
- Describe the distinguishing features of a cancer.
- Discuss the mechanism by which cancers evolve.
- Explain what is meant by "metastasis" and the mechanisms by which it occurs. List the mechanisms by which tumors cause harm. Explain the difference between the "grade" and the "stage" of a cancer. Describe the progressive stages in the evolution of breast cancer from normal to invasive ductal carcinoma. Define the following terms:
1. Cell differentiation
2. Benign tumor
3. Malignant tumor
8. Proto-oncogene and oncogene,
9. Tumor-suppressor gene (anti-oncogene)
10. Apoptosis and suicide gene
- Discuss risk factors for cancer and strategies for prevention, particularly with reference to the following:
4. Environmental exposures
5. Ultraviolet light
6. Viral and bacterial infections