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OBJECTIVES
After studying this chapter, you should be able to:
Present an overview of carcinogenesis and important biochemical and genetic features of cancer cells.
Describe important properties of oncogenes and tumor suppressor genes and their role in carcinogenesis.
Describe the important characteristics of cancer cells that distinguish them from normal cells.
Briefly describe the concepts of genomic instability, aneuploidy, and angiogenesis in tumor formation and growth.
Discuss the relevance of tumor markers.
Outline how understanding of the biology of cancer has led to the development of various new therapies.
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BIOMEDICAL IMPORTANCE
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Cancers constitute the second most common cause of death, after cardiovascular disease, in many countries. Approximately 9 million people around the world die from cancer each year, and this figure is projected to increase. Humans of all ages develop cancer, and a wide variety of organs are affected. Worldwide, the main types of cancer accounting for mortality are those involving the lung, stomach, colon, rectum, liver, and breast. Other types of cancers that lead to death include cervical, esophageal, and prostate cancers. Skin cancers are also very common, but apart from melanomas, are generally not as aggressive as those mentioned above. The incidence of many cancers increases with age. Hence, as people live longer, many more will develop the disease. Hereditary factors play a role in some types of tumors. Apart from great individual suffering caused by the disease, the economic burden to society is immense.
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SOME GENERAL COMMENTS ON NEOPLASMS
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A neoplasm refers to any abnormal new growth of tissue. It may be benign or malignant in nature. The term “cancer” is usually associated with malignant tumors. Tumors can arise in any organ in the body and result in different clinical features, depending on the location of the growth.
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Cancer cells are characterized by certain key properties: they (1) proliferate rapidly; (2) display diminished growth control; (3) display increased genomic mutations at the level of the nucleotide, small and large insertions and deletions (indels), and gross chromosomal rearrangements, duplications and loss; (4) display loss of contact inhibition in culture in vitro; (5) invade local tissues and spread, or metastasize, to other parts of the body; (6) are self-sufficient in growth signals and are insensitive to antigrowth signals; (7) stimulate local angiogenesis; and (8) are often able to evade apoptosis. These properties are characteristic of cells of malignant tumors. It is metastasis that is generally responsible for the deaths of patients who have cancer. By contrast, cells of benign tumors also show diminished control of growth, but do not invade local tissue or spread to other parts of the body. These points are summarized in Figure 56–1 and amplified on in Figure 56–2.
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