Up to one-quarter of all Americans will develop cancer in their lifetime, and many will die from it. Indeed, cancer is now the leading cause of death in the United States, recently surpassing heart disease.
We frequently think of cancer as a single disease, but it's actually many different diseases. Almost 200 different forms of cancer are known, and all are characterized by uncontrolled growth of cells. Normal controls on these cells have broken down and a "malignancy" has developed that invades and destroys healthy tissues.
What causes cancer? It's well known that it is initiated by certain carcinogens such as arsenic, asbestos, benzene and beryllium. But environmental factors such as air pollution and our lifestyle - the food we eat, whether we smoke or drink alcohol and so on - can also cause cancer.
How do these things actually cause normal cells to go bad? Cancer is a cellular disease so we have to look in detail at what goes on in the cells of our body. One of the main things is cellular division; cells divide, creating copies of themselves. This division is under the control of DNA - the basic molecule of life - a long molecule composed of two strands wound one around the other.
In human cells, DNA has 46 distinct regions called chromosomes that are arranged in pairs. They, in turn, contain approximately 25,000 genes, or segments of DNA that determine the structure of the protein that is needed for the growth, development and other vital functions of the body. Genes determine a person's characteristics.
DNA is protected most of the time, but it becomes particularly vulnerable when cells divide. When a cell receives a message to divide, many reactions are involved and all of them have to take place correctly for the cell to divide properly. Furthermore, division is initiated only when the cells received the proper signal, and the division stops when it received another (stop) signal. Cancer cells do not obey these signals.
How A Malignancy Forms
Cancer is initiated by a mutation at a specific locations along the DNA that makes up the gene. How mutations affect the DNA depends to a large degree on what are called cancer genes. There are two types of these genes, called tumor suppressor genes and proto-oncogenes. The tumor suppressors are associated with the cell's ability to divide; they stop division when it needs to stop (they also do other things). One of the best known is p53, which seems to be implicated in a large number of tumors. The proto-oncogenes stimulate growth, or cell division. Mutations change proto-oncogenes into oncogenes that allow uncontrolled growth.
From a simple point of view the process is as follows.
- A carcinogen, or other cancer-causing agent, alters the DNA sequence of the cancer gene.
- Mutations in tumor suppressor genes cause growth inhibiting protein usually coded by the genes to disappear allowing the cell to divide when it shouldn't.
- Mutations to the proto-oncogenes cause them to become very active, prompting them to grow when they shouldn't.
- Excess cellular growth leads to a mutant colony of cells that reproduces rapidly.
- Eventually a mass, or group of these cells, breaks free and leaks into the bloodstream and moves to another part of the body where they set up a new colony.
The actual process is, of course, much more detailed than this, and scientists still do not understand it completely. What we can see from this, however, is that it takes several different steps to produce a malignancy. Furthermore, although mutations take place continuously, few of them are actually serious, and the reason is that within the cell there are molecules that are continually repairing any mutations that occur. When a defective section of DNA is spotted, it is repaired, or if it is seen to be beyond repair, it is killed and deleted from the strand. So there are safeguards, and cancer has to get around these safeguards. Unfortunately, in many cases, it does. Let's look at the six "superpowers" that cancer cells need (and have) to get around problems such as these.
Six Superpowers that Cancer Cells Have and Need to Cause their Damage
- Normal cells require a signal to divide. Cancer cells ignore this signal; they continue to divide when they shouldn't.
- When growth is such that it should stop, a stop signal, or command, is sent out. Normal cells obey this signal; cancer cells do not. Such a command may, for example, be sent out by adjacent cells, when they are squeezed.
- When a healthy cell has built up several genetic defects it is usually programmed for destruction before it can cause any problems. Cancer cells are able to bypass this destruction.
- Like all cells, cancer cells also need oxygen and nutrients to survive. They come via blood vessels, and tumors don't have the appropriate ones. They are able, however, to "steal" them from nearby healthy cells.
- Healthy cells normally stop dividing after about 70 divisions. This is controlled by what are called "telomeres." Cancer cells need many more than 70 divisions to do their destruction, and they are able to manipulate the telomeres so that they have an infinite life.
- The last of the six superpowers is the one that makes cancer particularly deadly. Normal cells are generally confined to a certain region of the body. Cancer cells somehow disable the cellular mechanism that confines them. Because of this they can metastasize, or move to other parts of the body.
Cancer cells also have another problem to overcome. All humans have two sets of chromosomes, one from their mother and one from their father (with the exception of the X and Y sex chromosomes). So in a sense there is a back-up system in your body. This means that a mutation in one set is generally not enough to initiate cancer. In general it takes 4 to 10 mutations in a particular gene to transform it.
The p53 Cancer Gene
Earlier I mentioned the p53 cancer gene; it is a tumor suppressor gene, and it is very helpful in protecting us from cancer. Its importance is seen when doctors inspect tumors in detail. They have found that 50% of cancer tumors have defects, or mutations, in their p53 genes. To see why this is important we have to look at what p53 does. Basically, it's like an inspector; after cell division it thoroughly checks the new strips of DNA. In particular, it checks for errors and defects, and it makes sure that any that it finds are repaired. Furthermore, if it finds too many, it labels that section of DNA for destruction, and a new section if produced. Generally it does a good job, but it can get out of control occasionally and kill off good cells.
What You Can Do
This list is, of course, incomplete, but it should give you a good idea of what you can do.
- Early detection is obviously important - particularly before the cancer metastasizes and moves throughout your body.
- Avoid carcinogens as much as possible. Some of the major ones are: cigarette smoke, certain viruses, radiation and radioactive substances, asbestos, arsenic, air pollution, benzene.
- Diet. There is some controversy here, but general guidelines can be given. Some of them are: eat vegetables and fruit, avoid red meat, fiber is important, fish is helpful as are good fats such as omega 3 and other antioxidants.
- Both obesity and excess alcohol can lead to cancer.
- Other things: Vitamin D is important, and take a baby aspirin every day.