After studying this chapter, you should be able to:
- Present an overview of important aspects of the biochemical and genetic features of cancer cells.
- Describe important properties of oncogenes and tumor suppressor genes.
- Briefly describe the concepts of genomic instability, aneuploidy, and angiogenesis in tumors.
- Discuss the use of tumor markers for following responses to treatments and to detect recurrences.
- Appreciate that recent understanding of the biology of cancer has led to the development of various new therapies.
Cancers constitute the second most common cause of death, after cardiovascular disease, in the USA and many other countries. Approximately 6–7 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 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.
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.
Cancer cells are characterized by certain key properties: (1) they proliferate rapidly and display diminished growth control, (2) they display loss of contact inhibition in vitro, and (3) they invade local tissues and spread (metastasize) to other parts of the body. These properties are characteristic of cells of malignant tumors. It is the last property that is generally responsible for the deaths of patients who have cancer. Cells of benign tumors also show diminished control of growth, but do not invade local tissue or spread to other parts of the body. Other important properties of cancer cells are as follows: (1) they are self-sufficient in growth signals, (2) they are insensitive to anti-growth signals, (3) they stimulate local angiogenesis, and (4) they are often able to evade apoptosis. These points are summarized in Figure 55–1.
Six major features of cancer cells. Other important properties of cancer cells are shown in Figure 55–2. (With permission, After Hanahan D, Weinberg RA. The Hallmarks of Cancer. Cell 2000; 100:57).
Figure 55–2 shows a number of other important properties associated with cancer cells. These various points will be discussed below.