Understanding Breast Cancer:

If you or a loved one has been diagnosed with breast cancer, it's important to understand some basics: What is breast cancer and how does it happen?

In this section, you can learn about how breast cancer develops, how many people get breast cancer, and what factors can increase risk for getting breast cancer. You also can learn more about signs and symptoms to watch for and how to manage any fears you may have about breast cancer.

What is Breast Cancer?

Breast cancer is an uncontrolled growth of breast cells. To better understand breast cancer, it helps to understand how any cancer can develop.

Cancer occurs as a result of mutations, or abnormal changes, in the genes responsible for regulating the growth of cells and keeping them healthy. The genes are in each cell’s nucleus, which acts as the “control room” of each cell. Normally, the cells in our bodies replace themselves through an orderly process of cell growth: healthy new cells take over as old ones die out. But over time, mutations can “turn on” certain genes and “turn off” others in a cell. That changed cell gains the ability to keep dividing without control or order, producing more cells just like it and forming a tumor.

A tumor can be benign (not dangerous to health) or malignant (has the potential to be dangerous). Benign tumors are not considered cancerous: their cells are close to normal in appearance, they grow slowly, and they do not invade nearby tissues or spread to other parts of the body. Malignant tumors are cancerous. Left unchecked, malignant cells eventually can spread beyond the original tumor to other parts of the body.

The term “breast cancer” refers to a malignant tumor that has developed from cells in the breast. Usually breast cancer either begins in the cells of the lobules, which are the milk-producing glands, or the ducts, the passages that drain milk from the lobules to the nipple. Less commonly, breast cancer can begin in the stromal tissues, which include the fatty and fibrous connective tissues of the breast.

Over time, cancer cells can invade nearby healthy breast tissue and make their way into the underarm lymph nodes, small organs that filter out foreign substances in the body. If cancer cells get into the lymph nodes, they then have a pathway into other parts of the body. The breast cancer’s stage refers to how far the cancer cells have spread beyond the original tumor (see Stages of Breast Cancer table for more information).

Breast cancer is always caused by a genetic abnormality (a “mistake” in the genetic material). However, only 5-10% of cancers are due to an abnormality inherited from your mother or father. About 90% of breast cancers are due to genetic abnormalities that happen as a result of the aging process and the “wear and tear” of life in general.

While there are steps every person can take to help the body stay as healthy as possible (such as eating a balanced diet, not smoking, limiting alcohol, and exercising regularly), breast cancer is never anyone's fault. Feeling guilty, or telling yourself that breast cancer happened because of something you or anyone else did, is not productive.

Stages of Breast Cancer:

Stage IV    The cancer has spread — or metastasized — to other parts of the body.

Breast Cancer Statistics:

• Breast cancer incidence in women in the United States is 1 in 8 (about 13%).

• In 2008, an estimated 182,460 new cases of invasive breast cancer are expected to be diagnosed in women in the U.S., along with 67,770 new cases of non-invasive (in situ) breast cancer.

• About 1,990 new cases of invasive breast cancer will be diagnosed in men in 2008. Less than 1% of all new breast cancer cases occur in men.

• From 2001 to 2004, breast cancer incidence rates in the U.S. decreased by 3.5% per year. One theory is that this decrease was due to the reduced use of hormone replacement therapy (HRT) by women after the results of a large study, called the Women’s Health Initiative, were published in 2002. These results suggested a connection between HRT and increased breast cancer risk.

• About 40,480 women in the U.S. are expected to die in 2008 from breast cancer, though death rates have been decreasing since 1990. These decreases are thought to be the result of treatment advances, earlier detection through screening, and increased awareness.

• For women in the U.S., breast cancer death rates are higher than those for any other cancer besides lung cancer.

• Besides skin cancer, breast cancer is the most commonly diagnosed cancer among U.S. women. More than 1 in 4 cancers are breast cancer.

• Compared to African American women, white women are slightly more likely to develop breast cancer, but less likely to die of it. One possible reason is that African American women tend to have more aggressive tumors, although why this is the case is not known. Women of other ethnic backgrounds — Asian, Hispanic, and Native American — have a lower risk of developing and dying from breast cancer than white women and African American women.

• As of 2008, there are about 2.5 million women in the U.S. who have survived breast cancer.

• A woman’s risk of breast cancer approximately doubles if she has a first-degree relative (mother, sister, daughter) who has been diagnosed with breast cancer. About 20-30% of women diagnosed with breast cancer have a family history of breast cancer.

• About 5-10% of breast cancers are caused by gene mutations inherited from one’s mother or father. Mutations of the BRCA1 and BRCA2 genes are the most common. Women with these mutations have up to an 80% risk of developing breast cancer during their lifetime, and they often are diagnosed at a younger age (before age 50). An increased ovarian cancer risk is also associated with these genetic mutations. Men with a BRCA1 mutation have a 1% risk of developing breast cancer by age 70 and a 6% risk when they have a BRCA2 mutation.

• About 90% of breast cancers are due not to heredity, but to genetic abnormalities that happen as a result of the aging process and life in general.

• The most significant risk factors for breast cancer are gender (being a woman) and age (growing older).

Breast Cancer Risk and Breast Cancer Risk Factors:

By now you may be familiar with the statistic that says 1 in 8 women will develop breast cancer. Many people misinterpret this to mean that, on any given day, they and the women they know have a 1-in-8 risk of developing the disease. That’s simply not true.

In reality, about 1 in 8 women in the United States — or 13%, or 13 out of every 100 — can expect to develop breast cancer over the course of an entire lifetime. In the U.S., an average lifetime is about 80 years. So, it’s more accurate to say that 1 in 8 women in the U.S. who reach the age of 80 can expect to develop breast cancer. In each decade of life, the risk of getting breast cancer is actually lower than 13% for most women.

People tend to have very different ways of viewing risk. For you, a 1-in-8 lifetime risk may seem like a high likelihood of getting breast cancer. Or you may turn this around and reason that there is a 7-in-8, or 87.5%, chance you will never get breast cancer, even if you live to age 80. How you view risk often depends on your individual situation — for example, whether you or many women you know have had breast cancer, or you have reason to believe you are at higher-than-normal risk for the disease — and your usual way of looking at the world.

Even though studies have found that women have a 13% lifetime risk of developing breast cancer, your individual risk may be higher or lower than that. Individual risk is affected by many different factors, such as family history, reproductive history, lifestyle, environment, and others.