Breast Cancer

Overview

Each year, about 215,000 women in the United States are diagnosed with invasive breast cancer. And each year, the U.S. death rate from this disease is around 40,000. (Lung cancer is the only cancer that kills more women.) Additionally, about 58,000 women each year are diagnosed with noninvasive cancers, specifically ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). DCIS is a non-invasive cancer that may or may not progress to become invasive cancer. LCIS is an area of abnormal tissue growth in the lobules of the breast. This condition is not a true cancer, but having it puts you at a higher lifetime risk of developing cancer. Approximately 1,600 men are diagnosed in the United States each year, too--and often at a late stage, since men typically do not schedule regular mammograms or practice self-examination.

Like all cancers, breast cancer arises from the abnormal growth of cells, which may progress into a malignancy. Unless checked by treatment, invasive cancer cells travel through the blood and lymph system to different parts of the body, a process called metastasis.

For patients with noninvasive DCIS, the five-year disease-free rate is 97 to 98 percent. For patients with invasive early-stage cancer that is confined to the breast, the five-year disease-free rate exceeds 80 percent. This latter statistic in particular bears witness to the effectiveness of current treatments, which may include removal of the breast (mastectomy), removal of the mass and surrounding tissue (lumpectomy), chemotherapy, and hormone and radiation therapy. Each person's prognosis is based on tumor type and size, the aggressiveness of the cancer, the patient's age, and whether the cancer has spread beyond the breast, among other factors.

This section includes information on:

• Need-to-know-anatomy
• Causes
• Risk factors
• Breast cancer types

Need-to-know anatomy

In women, each breast is a milk-producing organ consisting of 15 to 20 lobes, or areas of glandular tissue that radiate from the nipple in much the same way that the petals of a flower radiate from its center. The lobes consist of smaller lobules, the glands that produce the milk. Hollow tubes, or ducts, transport milk from the lobules to the nipple. The connective tissue that supports these structures is known as stroma. In women of childbearing age, the majority of breast mass consists of fibrous and glandular tissue. After menopause, this glandular tissue tends to be replaced by fatty tissue.

The breasts also contain networks of lymph vessels, small tubes that circulate lymph, a fluid that carries disease-fighting white cells throughout the body. These vessels connect to lymph nodes, immune-system organs located mainly in the underarm area (axilla) and near the chest wall and over the collarbone and neck region. The lymph nodes store white cells and filter out bacteria and cancer cells.

Causes

No one knows precisely what causes the disease. Indeed, about 4 out of 5 women diagnosed with breast cancer have no family history of the illness, and many have no known risk factors. Still, women with certain characteristics are more prone to developing breast cancer. Postmenopausal women, for instance, are more likely than young women to be affected. For more on this, see our section on risk factors.

But regardless of how a breast cancer arises, it tends to spread (metastasize) by cells breaking away from the original tumor and traveling through the bloodstream or lymphatic system to remote parts of the body, where they grow into new tumors. If not checked by treatment, cancers of the breast, for instance, often invade the brain, liver, and bones.

Risk factors

Researchers have linked a number of factors with a higher risk of breast cancer. Yet most women who are diagnosed have none of them. What does that mean for you? It means you should be vigilant about getting mammograms regardless of whether you have known risk factors. And your vigilance should grow as you get older, since the risk of breast cancer rises with age and is greatest after age 60.

Some risk factors for breast cancer, such as starting menstruation before age 12, obviously cannot be changed. For more on these, see below. For those risk factors you can change, such as keeping your weight down, see our section on prevention.

Risk factors include:

• Belonging to a family with a strong history of breast cancer; the more first-degree relatives--mother, sister, or daughter--who have had the disease, particularly before age 50, the greater your own chances of getting it. Your risk also increases if a male member of your family has been affected or you have relatives with both breast and ovarian cancer.
• Having an inherited mutation in the genes that normally help regulate cell growth: BRCA1 and BRCA2 gene mutations increase your lifetime risk to between 40 percent and 80 percent. Other genetic mutations have also been associated with breast cancer.
• Having previously had breast cancer, or having one of two conditions in which abnormal cells are found in the breast, including atypical ductal or lobular hyperplasia and lobular carcinoma in situ (LCIS).
• Beginning menstruation before age 12 or reaching menopause after age 55, both of which increase a woman's lifetime exposure to estrogen. More than five to 10 years of hormone replacement therapy (especially the estrogen-progesterone combination) after menopause also may put women at greater risk. Men who have had disease characterized by high levels of estrogen, including cirrhosis of the liver and Klinefelter's syndrome, a genetic condition, appear to be more likely to develop breast cancer.
• Having a first pregnancy after age 35.

Breast cancer typing

Breast cancers are classified into types. The type is based on such criteria as the place where the cancer originated in the breast and its capacity to spread to other parts of the body. Ductal cancers start in the breast ducts; lobular cancers begin in the lobules. In situ (in place) cancers, also known as noninfiltrating, noninvasive, or Stage 0 cancers, are confined to the lobules or ducts. Some of these will become invasive and break out of the ducts and lobules to invade other tissues. But other in situ lesions don't seem to ever become invasive, which is why some experts say in situ"cancers" are really precancerous. Noninvasive cancers occur less often than invasive ones.

Common types of breast cancer:

• Ductal carcinoma in situ (DCIS): Abnormal cells have formed within the ducts but have not spread beyond. Women with this condition have a considerably higher risk of developing invasive cancer. Although DCIS is not invasive it is generally treated, with some combination of surgery, radiation, and hormonal therapy.
• Infiltrating, or invasive, ductal carcinoma: By far the most common invasive breast cancer, IDC involves ductal cancer cells that have moved beyond the ducts to other tissues.
• Infiltrating, or invasive, lobular carcinoma: Abnormal cells originating in the lobules have moved beyond the lobules into other tissues.

Several less common types of cancers also occur in the breast. These include Paget's disease, which affects the nipple and areola and is characterized by crustiness, itching, burning, or oozing; inflammatory breast cancer, which is highly aggressive and causes the breast to redden and swell; and mucinous carcinoma, in which the tumor has a jellylike character and the prognosis is better than for other invasive breast cancers.

Precancerous conditions:

• Lobular carcinoma in situ (LCIS): Women with this condition have a higher risk of developing cancer at some point in their lives. Options for women with LCIS include close observation, prophylactic mastectomy, or chemoprevention with tamoxifen.
• Atypical ductal or lobular hyperplasia: Women with these conditions also are at an increased risk of developing breast cancer.