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What is cancer?

"Cancer" is the general name for a group of more than 100 diseases that affect the body at a cellular level. Although there are many kinds of cancer, they all start because abnormal cellsCell:
The basic structural and functional unit of all organisms.
divide and grow out of control. 

Normal cells grow, divide and die and are replaced by new cells. Cancer cell growth is different from that of normal cells. Instead of dying, cancer cells continue to grow and form new, abnormal cells. These abnormal cells can lump together to form a mass of tissue called a tumourTumour:
An abnormal mass of tissue that occurs when cells divide more than they should or do not die when they should. Tumours may be benign (not cancer) or malignant (cancer). A tumour is also called a neoplasm.

Cancer cells can also invade (grow into) other tissues. This is uncontrolled growth, because the cell growth doesn’t stop when an adequate number of cells are developed, like in normal cells.

Cancer cells can also leave their original (primary) location in the body, for example the breast, and travel to other parts of the body and grow there, for example the bones. When cancer spreads in this way, the condition is called metastasisMetastatic (metastases):
The spread of cancer from its original (primary) location to another part of the body. A tumour that is formed by cancer cells that have spread to another part of the body is called a “metastatic tumour” or a “metastasis.”

Some conditions have cells that grow out of control, but cannot invade or spread to other tissues and organs. These are benignBenign:
Not cancerous. This is also referred to as non-malignant.
and their growth is confined to a specific area. Only cells that are able to spread are considered cancer.

How does cancer develop?

Cells become cancerous (or malignantMalignant:
) because of damage to their DNADNA:
Short for Deoxyribonucleic acid. DNA is found in the cells of our bodies. It contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. Your DNA contains genetic information that is unique to you.
—this is called a cell mutationMutation:
Any change in the DNA sequence of a cell. Mutations can be harmful, beneficial, or have no effect. Certain mutations may lead to cancer or other diseases.
. Most mutations develop after you are born. There are many factors that can cause a mutation, including smoking, exposure to hormones, radiation and cancer-causing chemicals, being overweight or obese, and a lack of physical activity. In a small number of cancers, the cancer results from a mutation that is inherited from one or both parents.

In a normal cell, when DNA gets damaged the cell either repairs the damage or the cell dies. In cancer cells, damage to the DNA prevents the cell from repairing or dying. Instead, this cell goes on making new cancer cells.

Cancer is a disease with a long latencyLatency:
The time from the start of a disease to when its symptoms show. A latent condition is present in the body but does not cause symptoms to show in the person.
period. This means that it may take years from the time of the first mutation to when signs of the disease appear. This is why cancer screeningScreening:
The search for diseases such as breast cancer in people without symptoms. Mammography is an important tool for breast cancer screening and earlier detection.
(for those cancers we are able to screen) is so important: to detect cancer earlier, before we can see or feel it.


American Cancer Society. What is cancer? Accessed May 29, 2014