What Is Cancer?

Excerpted from
The Answer to Cancer
By Carolyn D. Runowicz, M.D., Sheldon H. Cherry, M.D., Dianne Partie Lange

Every cell in the body is programmed to perform a certain job, depending on which organ it is part of. With the exception of brain and nerve cells, the rest continually develop, divide, die, and are replaced with newly formed cells.

It's believed that cells replicate a finite number of times, though just what determines their life spans remains a mystery. In any event, if the genetic machinery that directs a cell's division to proceed on a predetermined schedule goes awry, the cell may continue growing, and at a faster rate than normal. Similarly, a cell that experiences a malfunction in its genetic program to self-destruct may keep dividing indefinitely, rather than dying.

Nobel prize-winning scientist H. Robert Horvitz, Ph.D., an expert in the genetic intricacies of normal cell death, succinctly describes cancer as a change in the equilibrium between cell division or growth and cell death. "If you have too much cell division, you get an increase in cell number; if you have too little cell death, you also get an increase in cell number," Dr. Horvitz explains. "Either can lead to cancer."

Cells divide too often or refuse to die because of a genetic error, and usually more than one. Fortunately, the body has the ability to protect itself against a cell that contains flawed genetic messages. For instance, natural killer cells-which are components of a healthy immune system-will detect and eliminate a mutated, misbehaving cell. But sometimes the body's search-and-destroy mechanisms fail, and a malformed cell continues to divide, generating more and more copies of itself.

Although these renegade cells differ slightly from one another, they tend to cluster together, forming a mass or tumor. On the whole, they're an aggressive bunch, bullying and pushing their way into healthy tissues. Eventually a tumor can become so large that the affected organ can't do its job. Or a tumor may press on neighboring structures, obstructing some vital function or causing pain.

What's more, tentacles of the cancer cells can extend from the tumor into adjacent tissues, as well as into blood and lymph vessels. Sometimes the cells break free and spread through these circulating channels to distant organs, where they form more clusters of abnormal cells and a secondary cancer. This spreading process is known as metastasis.

The further cancer progresses, the less likely it is to be stopped. Once it has spread, or metastasized, to other parts of the body, successful treatment becomes very difficult.

Not All Cancers Are Alike

The progression from that first cluster of abnormal cells to a detectable tumor may take years. Cancer cells, being outsiders, follow no rules. They don't grow steadily and smoothly in a coordinate way, like healthy cells with flawless genetic messages. Instead, they tend to rest and grow, rest and grow.

But some cancers, when they are in a growth stage, can become quite large quite fast. They develop and spread so quickly that they may not be discovered until they are so large that they produce life-threatening symptoms.

Even a single form of cancer can manifest many different ways. For instance, one man may have prostate cancer all his life, but it grows so slowly that it doesn't produce symptoms and never spreads beyond his prostate gland, where it began. In fact, his cancer may remain undetected until he dies from some other cause. Another man may learn that he has advanced prostate cancer less than a year after a normal screening test. Ultimately, he may die from the disease.

Whether they grow quickly or slowly, not all tumors can be felt. If one is buried deep within the chest or abdomen, for instance, a person will have no clue that it's there unless it begins to interfere with some vital function or produces symptoms.

Fortunately, researchers have developed screening tests to find these hidden cancers before they reach advanced stages, as well as to detect abnormalities before they become full-fledged cancers. They're called screening tests because they're performed on healthy people who have no symptoms, for the sole purpose of looking for cancer or a condition that could lead to cancer. Screening tests that detect precancerous conditions are an essential part of cancer prevention. We will discuss tests that doctors now use, and those that researchers still are perfecting, throughout this book.

Recognizing the Enemy

It has been said that cancer is more than 100 different diseases because it varies according to the type of cell that's involved and the organ that is home to those cells. Despite this inherent diversity, all cancers share four fundamental characteristics.

1. CANCER BEGINS WITH THE BODY'S OWN CELLS. The cause-that is, whatever alters the genetic message within a cell- may come from outside the body. But the tumor itself is a cluster of cells.

2. THE CELLS GROW OUT OF CONTROL AND DON'T DIE. If a cancer is not detected and removed-or if its growth is not stopped with chemotherapy or radiation therapy-the cells will continue to divide.

3. THE CELLS FROM THE TUMOR MAY EXTEND INTO SURROUNDING TISSUES AND ORGANS, OFTEN DESTROYING THEM IN THE PROCESS. Even if this occurs, a cancer may not be fatal. The key is to excise all or part of the affected tissue, removing any trace of cancer cells. As extra insurance, this surgery often is followed by chemotherapy or radiation therapy to kill any cells that may have escaped detection.

Later in the book, you'll learn how some drugs can help prevent a recurrence of cancer when taken after treatment for the disease. Doctors refer to this as chemoprevention. They use the same term to describe drugs that stop the development of cancer in the first place.

4. THE CELLS CAN TRAVEL FAR FROM THE ORIGINAL TUMOR. Eventually, cancer cells enter the circulatory and lymphatic systems. From there, they spread to other areas of the body and begin to grow at those distant sites.

Because some 200 different kinds of cells exist in the body, doctors identify cancers according to the cells from which they originate. Every cell falls into one of four general categories:

• Epithelial cells, which comprise skin and line the passageways of the breasts, lungs, stomach, intestine, bladder, ovaries, uterus, and prostate

• Connective tissue cells, such as those that form cartilage, bone, muscle, and blood vessels

• Blood-forming cells, which make up the bone marrow

• Nerve cells, which include those in the brain and the body

Let's suppose that a doctor diagnoses a patient with epithelial carcinoma. In layperson's language, this means a cancer that involves the epithelial cells. Doctors also may describe tumors according to the function of the cells. For instance, an adenocarcinoma arises from secreting glands, such as those that form in the breasts from epithelial tissue.

Tests are available to determine the aggressiveness of a particular cancer, as well as appropriate treatment options. Although these tests are important, they can be done only after a cancer has been discovered. Researchers are working to identify markers that alert doctors to the presence of a cancer or precancer that consists of just a few cells. Then, even if the cancer is aggressive, the cells can be removed or destroyed before a tumor develops.

A good example of this type of test is the Papanicolaou smear, or Pap test, which has been in use since the 1950s. This routine screening test for women detects abnormal cells on the cervix that are likely to become malignant. More recently, researchers have been working on tests to examine breast fluid for cancer cells, and stool samples for abnormal cells from the colon lining. The tests are under evaluation to determine their accuracy in discovering precancerous conditions and their practicality for widespread clinical use.

How Cancer Begins

As complicated as cancer is, and as confusing and complex as the names of the many different kinds of cancer are, the simple fact is that the disease begins with a single cell. From there, it follows a well-choreographed process consisting of three key steps: initiation, promotion, and progression. Each of these plays a crucial role in cancer prevention. In particular, measures such as risk control, early detection, and chemoprevention are likely to be most effective during the first two steps.

The following discussion gets a bit technical, so you may want to skip over it for now and come back to it when you're reading about a specific aspect of cancer prevention. It provides the necessary background for understanding why some things protect against cancer and, perhaps equally important, why other things don't. If you understand how the disease develops in the first place, you'll be better able to take action to lower your risk.

Initiation

All cancers begin with a mistake within a cell's chromosomes, which serve as the containers of the cell's genetic material, or DNA (short for deoxyribonucleic acid). The mistake may appear in the chromosome itself, or it could turn up in a gene-a segment of DNA-within the chromosome.

DNA consists of a long chain of chemicals tightly wound within the chromosome. The strands of DNA in each of our 23 pairs of chromosomes contain between 30,000 and 40,000 genes.

While a mistake, or mutation, in a gene may be inherited from a parent, it's more likely to occur spontaneously in the course of cell division. Or it could be the result of some external factor. A physical injury such as bombardment with radiation can cause a mutation. So can a viral infection or chronic inflammation. For example, in ulcerative colitis-inflammation of the intestinal tract-cells divide very rapidly, increasing the possibility for error. A mutation also can be linked to a chemical, like the ones in tobacco smoke.

Chromosome with DNA

DNA (deoxyribonucleic acid) is a thread of four precisely ordered CHEMICALS COILED UP WITHIN EACH CHROMOSOME IN A CELL'S NUCLEUS. (EACH CELL CONTAINS 46 CHROMOSOMES.) THE FOUR CHEMICALS THAT MAKE UP DNA JOIN EACH OTHER, FORMING A TWISTING, LADDERLIKE STRUCTURE DESCRIBED AS A DOUBLE HELIX. UNITS OF DNA ALONG THIS LADDER, OR GENES, CONTAIN A CODE THAT INSTRUCTS THE CELL TO MAKE A SPECIFIC PROTEIN.

Anything that's responsible for triggering a genetic mutation that eventually can turn into cancer is known as an initiator or a carcinogen. You'll learn more about carcinogens in part 2, when we discuss specific cancers.

The good news is, most of the mutations that affect DNA are corrected by the body's built-in repair mechanisms, which also are under genetic control. The injured DNA can be replaced with a healthy section, using what might best be described as a cellular patch kit. Enzymes that remove certain kinds of damage travel to the site of the mutation to make the necessary repairs.

Unfortunately, mutations also can occur in the genes that govern these repair mechanisms, as well as in the genes that control a cell's growth or death. In particular, mistakes in the genes responsible for cell growth, called oncogenes, can lay the groundwork for cancer. This is because as mutations accumulate, the opportunity for oncogenes to become hyperactive increases as well. A protein that's produced by oncogenes instructs cells to reproduce endlessly.

So far, scientists have identified more than 100 different oncogenes. Usually several take part in the cancer process. Sometimes they're switched on by external factors, such as substances in tobacco smoke and the ultraviolet radiation in sunlight.

Some oncogenes tend to be associated with certain cancers. One example is RAS, an oncogene that plays a role in colorectal cancer.

Mutations even appear in genes whose sole purpose is to stop tumors from forming and/or growing-hence the name tumor suppressor genes. One such gene that is especially well-known to cancer researchers is the p53 gene. A mistake, or mutation, in this gene is present in more than 50 percent of all tumors. You'll learn more about the p53 gene, along with the 17 or so other tumor suppressor genes, later in this book.

Promotion

For cancer to develop and grow, two events must take place: a change in a gene that affects cell growth, and exposure to something that promotes cell growth. This so-called two-hit theory explains why not all women who inherit a breast cancer gene actually develop breast cancer and why not all smokers get lung cancer.

More than likely, several genetic mutations are necessary to trigger cancer. As scientists continue to discover and map genes, they also will be able to determine which combinations of genetic errors affect a person's cancer risk.

A promoter is something that speeds up the pace of cell division, which can create more genetic mutations and deliver the second hit that leads to cancer. A promoter may be a hormone such as estrogen or a toxic substance such as a chemical in tobacco smoke. Researchers believe that obesity and poor diet may act as promoters, though the mechanisms behind them aren't clear. Some factors, like radiation, can play the dual roles of initiator and promoter.

Fortunately, from a prevention point of view, some substances can interfere with cancer promotion. For instance, certain types of dietary fiber curtail the absorption of carcinogens in the intestine. In laboratory experiments, antioxidants such as vitamins A, C, and E act as anticarcinogens. On the other hand, deficiencies in these nutrients may contribute to certain cancers.

The cancer process still can turn around at the promotion stage, depending on the amount of genetic damage. But scientists don't know for certain when this window of opportunity closes. Until they can answer this question, avoiding promoters remains an important aspect of cancer prevention.

Progression

The term progression refers to the out-of-control growth of abnormal cells that is the basis of all cancers. As explained earlier, the cells accumulate to form a tumor, and the tumor keeps growing, possibly extending into adjacent tissues. In addition, cells may spread to other parts of the body, forming clusters there.

How quickly a cancer progresses is determined in part by genetic programming. It also is influenced by conditions in the body, such as the presence of certain hormones. Even once progression begins, a vigilant immune system still may destroy cancer cells, significantly interfering with the disease process, if not stopping it entirely. Cancer growth may be so slow that the malignant cells never cause a problem. In support of this fact, it's estimated that cancer is present in the organs of 10 to 15 percent of people who die from other causes.

Prevention Is Paramount

Now that you have a basic understanding of what's involved in the cancer process, you can see how prevention could be your best defense against the disease. You have many options for stopping cancer before it gains a foothold. For instance, you can limit your contact with substances that initiate or promote the disease. You can enhance the body's immune defenses and cellular repair systems. Pinpointing and treating precancers offer another avenue of attack. So, too, does turning on or off the various mechanisms that drive cell growth.

Some of these preventive measures are available now. Many more are on the frontier of cancer prevention. We'll explore them in depth in the chapters that follow.