Cancer has affected the lives of each and every one of us alive today. Many people have know someone with cancer, yet even those who haven’t have been bombarded with constant reminders of its terrible threat. Although cancer is often referred to as a single condition, it actually consists of more than 100 different diseases, all characterized by the uncontrolled growth, reproduction, and spread of abnormal body cells.
All of these diseases are individually unique, yet the basic processes that produce cancers are very similar (Ruddon, 1995). The human body consists of over 30 trillion cells, living in a complex, interdependent harmony. They regulate each other’s proliferation; normal cells reproduce only when instructed to do so by other cells in their vicinity. This constant collaboration ensures that each tissue maintains a certain size and function that is exactly what the body needs.
Cancer cells, on the other hand, violate the entire process. Not only do they ignore the body’s controls on proliferation, they possess the ability to invade nearby tissues, and may even metastasize – migrate and form tumors in distant sites of the body. How do cancer cells achieve this? For decades, this question plagued scientists everywhere. But over the last 20 years, scientists have uncovered a set of basic principles that govern the development of cancer ( Brock, 1993).
Within each cell lies a structure called a nucleus which contains strips of material known as DNA (dioxyribonucleic acid.) Each of these strips is divided into hundreds of genes, which are the codes and templates for all the functions of the human body. Each gene specifies a sequence of amino acids that must be linked together to make a particular protein; the protein then carries our the work of the gene. Two types of genes, which are only a small fraction of the genetic material, play particularly important roles in triggering cancer.
Proto-oncogenes induce cell growth and reproduction, while tumor suppressor genes inhibit it. Together, they carefully control the proliferation of cells. However, if a proto-oncogene is mutated, it can become a carcinogenic oncogene, driving excessive multiplication. Tumor suppressor genes, on the other hand, contribute to cancer when they are inactivated by mutation (Ruddon, 1995).
Luckily, cancerous tumors are not caused by one little mutation in one cell – they are caused by multiple mutations in a number of the cell’s growth-controlling genes. The number of mutations necessary can be as low as two or quite high, depending on the specific type of cancer. Generally, these mutations occur either from mistakes during cell reproduction, or due to DNA damage caused by carcinogens such as tobacco, certain poisons, and UV rays. So, why don’t we all get cancer from these things right away? Consider that one of your cells is damaged by poison and becomes mutated.
In order for this cell to turn into a cancer cell, the rest of the necessary mutations must also occur in this very same cell. This in itself, is fairly unlikely. It normally takes decades for an incipient tumor to collect all the mutations required for it’s malignant growth, which explains why the average age for cancer diagnosis is 67 (Ruddon, 1995). Why, then, do some individuals contract cancer before the typical age of onset? In many cases, this is explained by the inheritance of a mutation in a critical growth controlling gene.
Typically, this mutation would be a very rare event. However, in this individual, the mutation is present in ALL the cells of the body, instead of in some randomly stricken cell. So, the process of tumor formation skips it’s first, slow step. No one can actually inherit cancer; rather, they inherit a predisposition to develop a cancer, which is why cancers do tend to run in families, but not all family members are stricken (Brock, 1993).
The outlook for people with cancer has improved steadily since the beginning of the 20th century, when few cancer victims survived for very long. Today, 51% of cancer patients survive for 5 years or more, and the American Cancer Society estimates that an additional 25% of cancer deaths could be prevented with earlier diagnosis and treatment (ACS homepage). However, one in three people in the United States will eventually develop some type of cancer, so routine screening for early detection should be an important part of everyone’s lives (Ruddon, 1995). The earlier cancer is diagnosed and treated, the better the chance of it’s being cured.
Some cancers, such as breast and skin cancers, can be detected by routine self-examination before they become too serious, while others are only detected by more complicated methods. Either way, early diagnosis appears to be the key to survival.Sources:Ruddon, Raymond W. 1995.
Cancer Biology, 3rd ed.New York: Oxford University Press.Brock, D.J.
H. 1993. Molecular Genetics for the Clinician. 1st ed.New York: Cambridge University Press.