What is cancer?

Cancer is a disease where damaged cells in the body start dividing out of control, making more and more damaged cells. These damaged cells come together to form a lump called a tumor.

Tumors can be benign or malignant. Cells in a benign tumor keep to themselves and don’t bother the other cells around them. Malignant tumors are cancer and cause trouble to cells around them. They can also spread to other parts of the body, causing trouble there too. Cancer can happen in different parts of the body. It can occur in organs like the kidney or brain. It can also occur in the blood cells in the bone marrow.

The human body possesses numerous forms of checks and balances. The immune system plays a major role in maintaining that equilibrium. One of its roles is to evaluate human cells’ surfaces by tasting cell surfaces by way of antigens exposed on the outside of cells. The immune system is then able to identify these tastes as “family” or “foreign." Cells can be identified as foreign to regions of the body, or to the human body altogether. Further checks and balances can communicate with cells to regulate cellular growth and division. When human cells significantly deviate from protocol, a signal is communicated to the cell to initiate cell death.

But, when mutations occur, certain cells may possess unique abilities to evade the immune system. Three specific traits a cancer cell will likely possess are:    

  1. The ability to be viewed by the immune system as non-foreign.
  2. The ability to grow and divide regardless of inhibitory signals from the immune system.
  3. The ability to defy messages from the immune system that signal cell death.

Cancers are not all equally aggressive in nature. Some may have other unique mutations allowing for slow or more aggressive growth, and other mutations permitting them to spread to other regions of the human body. 

Cancer is the growth and spread of abnormal cells. Normal cells grow, divide, and die in an orderly fashion. During growth and development, they divide more rapidly, but in adults they divide only to replace worn-out or dying cells and to repair injuries. Cancer cells, however, do not behave like normal cells. They continue to grow and divide, forming masses of abnormal cells, called tumors. These masses can compress normal cells and interfere with their ability to function.

Not all tumors are cancerous, but if they do become cancerous, or malignant, cells can break off and travel through the bloodstream or the lymph system to other areas of the body. This is called metastasis, and once this happens, cancer is no longer curable. Cancer is named after the part of the body where it began.


Dr. Daniel Labow, MD
Surgical Oncologist

Cancer is a term used for diseases in which cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer cells can spread to other parts of the body either through the bloodstream or lymph systems.

The three most common cancers in men, women and children in the U.S. are as follows:

  • Men: Prostate, lung, and colorectal
  • Women: Breast, colorectal, and lung
  • Children: Leukemia, brain tumors, and lymphoma

Cancer is a leading cause of death worldwide. It accounted for 7.4 million deaths (around 13% of all deaths) in 2004.

Lung, stomach, liver, colon, and breast cancer cause the most cancer deaths each year.

Deaths from cancer worldwide are projected to continue rising, with an estimated 12 million deaths in 2030.

There are more than 100 different types of cancer. Most are named for the organ or type of cell in which they start.

Cancer types can be grouped into broader categories. The main categories include:

  • Carcinoma - cancer that begins in the skin or in tissues that line or cover internal organs.
  • Sarcoma - cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.
  • Leukemia - cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood.
  • Lymphoma and myeloma - cancers that begin in the cells of the immune system.
  • Central nervous system cancers - cancers that begin in the tissues of the brain and spinal cord.

The etiology can be complex, and it is often impossible to assign a specific cause for a specific cancer. Many factors are known to increase the risk of cancer, including tobacco use, infection, radiation, lack of physical activity, poor diet, obesity, and environmental pollutants.

Cancer can be detected by the presence of certain signs and symptoms, screening tests, or medical imaging. It can be diagnosed by microscopic examination of a tissue sample.

Cancer is usually treated with chemotherapy, radiation therapy and surgery.

The chances of surviving the disease vary greatly by the type and location of the cancer and the extent of disease at the start of treatment.

Cancer is abnormal growth. Normally the body's cells "talk" to one another  through a complex signalling system that keeps our organ systems in balance by controlling cell growth. A cancer cell's signalling system is broken and they  can no longer hear cell talk, and the signals to stop growing, and grow uncontrollably. They divide more often than normal cells and accumulate in the body as lumps or masses of tumor cells that, if unchecked, eventually crowd out normal organ function.


Dr. William D. Knopf, MD
Cardiologist (Heart Specialist)

A term for diseases in which abnormal cells in the body divide without control. Cancer cells can invade nearby tissues and can spread to other parts of the body through the blood and lymphatic system, which is a network of tissues that clears infections and keeps body fluids in balance.

This answer is based upon source information from the National Women's Health Information Center.

Dr. Scott A. Kamelle, MD
Gynecologic Oncologist

The word cancer refers to human cells that lose their ability to control growth. As a result, cancer cells continue to divide and ultimately develop into masses or tumors. These tumor cells then differentiate themselves even further from normal cells by having the ability to "travel" throughout the body unregulated. We refer to this as metastasis. Uncontrolled growth and travel are the core characteristics of a cancer cell.

Cancer begins when cells grow and divide uncontrollably. Normally, cells only divide to form new cells when the body needs them, and the body destroys old cells that are no longer functioning properly. Mutations in cell DNA can cause cells to grow and divide uncontrollably, or may prevent old cells from dying when necessary. The reasons these mutations occur are not known, but it is known that the mutations can either be inherited or acquired during life.

When extra cells accumulate and form a mass, it is called a tumor. Tumors can be benign or malignant. Benign tumors arise when abnormal cells accumulate, but do not possess the ability to invade other tissues and organs. This is why benign tumors are not cancerous. However, they can cause health problems by placing pressure on nearby organs, blood vessels, or nerves.

Malignant tumors, often referred to as cancer, are abnormal cells that have the ability to invade other tissues and organs. When cancer cells metastasize, or break away from the original cancer site (primary tumor), new tumors can form in other parts of the body.

Although cancer is usually referred to as a single disease or condition, it actually consists of more than 100 different diseases. These diseases can begin in virtually all parts of the body and all are characterized by the uncontrolled growth and spread of abnormal cells. As these cells divide too rapidly and grow without order, tumors or other abnormalities begin to form. Once it develops, cancer can spread to areas close to the original site. It can also spread to more distant sites in the body by moving through the blood or lymphatic system.

Cancer is a term used for diseases where some cells reproduce and grow abnormally (malignant changes), and have the ability to spread to other parts of the body. When cancer spreads to other parts of the body it is called metastasis. Cancer cells can spread to nearby parts of the body, or through the blood and lymph systems to more distant parts.

Cancers are named for the part of the body or the cell where they started; even when they spread to other parts of the body. For example, cancer that begins in the colon is called colon cancer, even when it spreads to the liver or other parts of the body.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.