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It can be devastating to be told that you have breast cancer. The condition is so common that you may already know at least one woman who has it. But you can still feel frightened and alone when you're the one who has been diagnosed with breast cancer.

Getting breast cancer will undoubtedly change your life. We know from women with breast cancer that, although you'll feel shocked, you'll probably want to learn about your condition. Many women with breast cancer also say that, once the shock fades, they often appreciate life more and feel more positive and optimistic.

• More women live with breast cancer than die from it.
• Breast cancer is the second most common cancer among women in the United States.
• Each generation of women has a better chance of surviving breast cancer than their mothers' generation.
• Different women will have different treatments, depending on what type of breast cancer they have and how they feel about treatments.
• Early breast cancer can usually be cured.
• There are two main types of treatments for breast cancer. Treatment that just affects your breast, such as surgery and radiation therapy, and whole-body treatment, such as chemotherapy and hormone treatment.
• Breast-conserving surgery (which removes only some of your breast) often works just as well as a mastectomy (which removes all of your breast).

To understand how breast cancer starts and how it is treated, it helps to know about your breasts.

In women, the breast is designed to make milk for babies. Milk is made in parts of your breast called lobules. Milk drains into the nipple through thin tubes, called ducts.

• The space between the lobules and milk ducts is filled with supporting tissue (called connective tissue).
• A layer of fat surrounds the connective tissue and lies between the milk-producing parts of the breast and the skin.
• This layer of fat contains blood vessels (which carry oxygen and food to the cells of the breast) and lymph vessels (which carry a fluid, known as lymph, back into the bloodstream). To read more, see What are lymph vessels?
• The part of the breast that is most likely to get a disease is the part that includes the lobules and the last drain duct (known as the terminal duct lobular unit).

Breast cancer starts in the cells lining the ends of the milk-producing glands (the lobules) and in the thin tubes that carry milk to the nipple (the ducts). Experts used to think that cancer started either in the lobules or the ducts, but we now know that it starts where the ends of the ducts meet the lobules.

Normally, cells grow, divide, die and get replaced in an orderly way. For example, when cells are damaged, as they are by everyday wear and tear, they get replaced. In cancer, however, the cells grow in a disorderly way. Cells grow on top of each other and don't stop growing when they touch other cells.

Cancer cells also look different from normal cells. This is because they grow faster and start dividing before they look like their parent cells. Often they look like immature versions of their parent cells. This chaotic growth is the start of cancer, and, as it continues, the cancer spreads to nearby tissues.

If these cells enter the blood vessels or lymph vessels, they can travel to other parts of the body and start growing there. When a cancer spreads, it is called metastasis.

Doctors give breast cancers different names depending on how far they have spread. If the cancer cells are contained within the ducts of the breast, this is called ductal carcinoma in situ (DCIS). If the cancer cells have spread outside the ducts of the breast to the surrounding tissue, this is called invasive breast cancer.

There are different types of invasive breast cancer.

• The most common type is early breast cancer, which means the cancer hasn't spread beyond the breast or nearby lymph nodes.
• If the cancer is large (around 2 inches or more across) or has spread to the skin, to the front of the chest, or to both the skin and chest, this is locally advanced breast cancer. The lymph nodes under the armpit might also have become matted together by the tumor.
• If the cancer has spread to another area in the body (such as the lungs or liver), this is advanced (mestatatic) cancer.

To learn more, see Types of breast cancer.

To figure out what type of breast cancer you have, your doctor will need to know how serious it is. Doctors call this staging.

Your doctor may also look at how much your cancer cells resemble normal breast cells when viewed under a microscope. Doctors call this grading.

Knowing the stage and grade of your cancer will help your doctor decide which treatments are best for you. To learn more, see Staging and grading breast cancer.

The first question many women ask is, "Why me?" There really is no answer to this question unless you are one of the very few women who get breast cancer because of inherited genes. All we can say is that your breast cancer is not your fault.

For most women, no cause for the cancer can be found. Doctors can tell you about risk factors rather than causes. Risk factors are things that increase your chance of getting a condition. The biggest risk factor for breast cancer is being older.

To find out more, see Risk factors for breast cancer.