What is Cancer?
Cells and the Genetic Code: The Origins of Cancer
Cells are the basic building block of life. All living tissues are made of cells. There are hundreds of different types of cells in the body. Each type has a specific function. Blood cells carry oxygen, nerve cells carry instructions, skin cells protect our bodies, and so on.
Illustration: Cells are very small. Packed together, six million blood cells (or cancer cells) are no larger than a strawberry seed.
Illustration: This strawberry illustrates how many cancer cells can fit in one strawberry seed.
All cells contain DNA, a special kind of molecule that contains our genetic code. DNA controls all of a cell's functions, including cell reproduction (growth). If the DNA is damaged in a certain way, the cell may reproduce uncontrollably. Uncontrolled growth is the beginning step in
Illustration: The first step in formation of cancer is damage to DNA, such as by a chemical, germ or radiation.
Substances that cause cancer-producing DNA damage are called carcinogens(carSIN-oh-gins). Carcinogens include a few specific viruses, some natural substances (tobacco, asbestos, etc), chemicals, and some types of radiation. The interval between exposure to a carcinogen and the development of cancer is usually years to decades. There are many carcinogens that affect humans. However, for most human cancers we cannot look back in time and identify a carcinogen or clear cause for the cancer. Indeed, most cancers in humans have no single dominant cause. Most cancers arise because of many factors, only one of which may be exposure to an identifiable carcinogen. The other factors include things like age, diet, lifestyle choices, and unique aspects of a personÕs genetic code that make him or her more vulnerable to developing cancer.
Illustration: Cancer cells grow slowly at first.
Cancer = Uncontrolled Growth + Ability to Spread
Cancer is defined by uncontrolled cell growth and the ability to spread and grow in other parts of the body.The first step in cancer formation is uncontrolled growth. This growth is very slow at first, and many cancers spend years or decades in this step before spreading.
The second step in cancer formation is the ability to spread to other parts of the body.Over time, growing cancer cells can change and become able to spread (metastasize) to other parts of the body. It is this ability to spread throughout the body that defines a cancer and that makes it a potentially life-threatening disease.
Illustration: Cultured Cancer Cells.
Some cancers grow very slowly and almost never spread; a good example is the common skin cancer basal cell carcinoma, which is almost 100% curable. Some cancers, however, have frequently spread before they are detected; this is often the case for cancers of the lung and pancreas.
Is Cancer One Disease or Many?
There are many different types of cancer. Doctors label cancers by their place of origin. Breast cancers start in the breast, lung cancers start in the lung, etc. Some are very curable and rarely a threat to life, while others are resistant to treatment and very lethal.
Cancers of the same type may look and behave similarly. For example, breast cancers in two different women may look very similar under the microscope and may be vulnerable to the same anti-cancer drugs (chemotherapy). These common features allow doctors to predict - within reason - how a given type of cancer will behave and how it may respond to treatment. This knowledge guides doctors in making treatment recommendations. However, despite these common features, every cancer is unique, and the outcome of one person with breast cancer cannot predict the outcome of another person with breast cancer.
Is Cancer a New Disease?
Popular theories suggest that cancer is caused by pollution and is a 'curse' on modern society. This is incorrect.
Some cancers are from human-made carcinogens, but most carcinogens are naturally occurring. Examples include tobacco, asbestos, and the cancer-causing viruses. Humans can make the unwise decisions to smoke tobacco and line buildings with asbestos, but these substances themselves are not new. Cancer is as old as life itself; it has been found in dinosaur fossils and in the mummified bodies of ancient humans.
Why is Cancer a Threat to Life?
Why do cancers threaten a patient's life? One way is by spreading to - and damaging - other organs in the body. Cancer that spreads to the lung can cause shortness of breath and pneumonia. Cancer that spreads to the brain can cause symptoms similar to a stroke.
Cancer has other effects that may not relate to spreading to and damaging a particular organ. Many cancer cells secrete chemicals or hormones that cause weight loss, weak bones, fevers, fatigue, a vulnerability to infections, and chemical imbalances in the blood.
Is Cancer Curable?