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What is breast cancer?

“Cancer” is the general name for a group of diseases that affect the body at a cellular level. Although there are many kinds of cancer, they all start because abnormal cells divide and grow out of control. These abnormal cellsCell:
The basic structural and functional unit of all organisms.
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.
. If the breast is the original (primary) location of a cancer growth or tumour, the condition is called breast cancer.

The breasts consist mainly of fatty tissue that contains thousands of tiny glands—or lobulesLobules:
Small glands in the breast that produce milk.
—whose function is to produce milk in a woman if she carries a pregnancy to term. They also contain mammary ductsDuct (mammary duct):
A hollow passage for gland secretions. There are ducts in the female and male breast.
, which transport milk from the lobules to the nipple.

Different types of breast cancer can occur in different tissues in the breast. Cancer that forms in the mammary ducts is called ductal carcinomaCarcinoma:
A malignant (cancerous) tumor that begins in the layer of cells that line the organs (called epithelial cells).
and is the most common type of breast cancer. When cancer occurs in the lobules, it is known as lobular carcinoma.

Breast cancer can also spread beyond the breast area if cells break off from the growth or tumour and travel through the blood stream or lymphatic systemLymphatic system:
A network of vessels that transports lymph fluid, a clear fluid that comes from your blood and bathes the tissues. It contains water, protein and minerals and white blood cells. The lymph passes through a series of filters, the lymph nodes, before rejoining the bloodstream.
to other parts of the body. This condition is called metastaticMetastatic (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.”
breast cancer.

Breast cancer is a complex disease and there are many factors that play a role in its development.  Some of the factors that increase breast cancer risk we have more influence over, such as diet, alcohol use, and exposure to certain chemicals in the environment. Other factors we have less influence over, such as geneticGenetic:
Related to or caused by the genes.
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.
that we inherit from our parents. Scientific evidence suggests that a combination of factors, rather than a single cause, influences the development of breast cancer. Learn more about the possible causes of breast cancer.

More research is needed to understand better how risk factorsRisk factor:
Anything that increases a person’s chance of developing a disease, such as cancer.
work together to result in the cell changes that lead to breast cancer. Research helps to improve our knowledge of breast cancer, giving us a stronger understanding of breast cancer risk and ways to try to reduce the risk.

Be Breast Aware

It's quite normal for your breasts to differ slightly in shape, size, and the way they feel, and to change during your menstrual cycle, in pregnancy and as you age. Many of the most common breast changes are not signs of breast cancer.  Canadian Breast Cancer Foundation encourages you to be breast aware – know how your breasts normally look and feel so that you are able to discuss any changes with a health care provider.



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

National Cancer Institute. Understanding Cancer Series. Accessed May 29, 2014

Quebec Breast Cancer Foundation. What is breast cancer? Accessed May 29, 2014