What is Cancer?

By Linda L. Isaacs, M.D.

Tumors are a collection of cells that are growing out of control. Tumors can be benign or malignant. Cells in a benign tumor are unable to spread to other locations in the body. Cells in a malignant tumor can spread. Malignant tumors are called cancer.

Most cancer experts believe that cancer arises from a single cell that begins to reproduce itself and grow abnormally. Most experts would agree that everyone creates cancer cells all the time, but we have mechanisms to get rid of them. These mechanisms are usually sufficient to dispose of all the cancer cells we make.

However, some people have weaker mechanisms for getting rid of cancer cells. They make cancer cells at the usual rate, but they are slow to destroy them. As an example, if the immune system is naturally weak or has been affected by medications, small cancer cells will not be eliminated and cancerous masses can develop.

For others, environmental toxins, metabolic issues, or genetic problems can cause more cancer cells to form than the disposal mechanisms can handle. Examples include cigarette smoking and exposure to toxic chemicals. You may have heard of people who smoked and lived to be 100 years old. Those people most likely had very powerful mechanisms for getting rid of toxins and of cancer cells, unlike their less fortunate neighbors.

How then does cancer impact the body? Well, either benign or malignant tumors can cause problems if they are in a bad location, where they interrupt important bodily functions. A tumor mass that grows to the point where it blocks the intestine will require treatment, regardless of whether it is benign or malignant.

Malignant tumors sometimes put out waste materials that can make patients sick. As an example, some cancers emit chemicals that interfere with appetite. And there are a few cancers that secrete hormonally active substances that cause problems throughout the system.

However, the most common life-threatening issue is metastatic disease, cancer that has spread. Cancer cells can break loose from the original tumor, and travel through the blood or lymphatic system to lodge in other parts of the body. There, they can grow and interfere with the function of the tissue where they landed. For example, if cancer cells have spread to the liver, eventually the liver may not be able to perform its important work because too many liver cells have been replaced by cancer cells. Fortunately, the functional reserve in organs like the liver and lungs is quite large, so there is usually time for treatment when metastases have been found in these organs.

Next Section: How Does Cancer Develop?