What Is Breast Cancer?

Breast cancer is cancer that affects the breast. The vast majority of breast cancer occurs in women, although men can develop breast cancer too.

'Cancer' is the name for a group of diseases in which the body's cells are changed in appearance and function. Such abnormal cells can grow out of control and form a mass or 'tumor.' When abnormal cells originate in the breast tissue, the mass is called a breast tumor.

A breast tumor is considered benign if it is limited to a few cell layers and does not invade surrounding tissues or organs. Yet if the tumor spreads to surrounding tissues or organs, it is considered malignant, or cancerous. Carcinoma is the term used to describe most common cancers that arise from epithelial (surface or lining) tissues. By contrast, sarcoma is the term used to define tumors that arise from bone, muscle, fat, or connective tissue.

The breasts are, in essence, a collection of fatty tissue and glands that have been adapted to secrete milk after a woman gives birth. The glands that produce milk are called lobules and the tubes that connect them to the nipples are called ducts. Correspondingly, carcinoma of the breast develops when malignant changes occur in the cells that line the lobules or, more commonly, the ducts.

There are two major types of breast cancer:
lobular carcinoma, and ductal carcinoma.

They can be either invasive (spreading) or noninvasive (generally known as 'in situ' - confined to the original site). The majority of breast cancers (70% - 80%) arise from the ducts, which make up the bulk of breast tissue. Since lobular and ductal cells are found in the glandular tissues of the upper, central, and outer regions of the breast, this is where most breast cancers occur. Breast tumors rarely arise in the fatty or nonglandular tissues. Such tumors, when they appear, are usually sarcomas.

Cells from the tumor may break away, travel, and grow within other parts of the body. This process is known as metastasis. Breast cancer often metastasizes to sites such as the lung, bone, liver, and brain. If breast cancer is detected at an early stage - for example, before metastasis - it usually can be cured; however, as the disease progresses, the possibility of effective treatment is diminished. Fortunately, though, many breast "lumps" are caused by benign breast diseases that do not spread beyond the breasts and are not life-threatening.

What Causes Breast Cancer?

The exact cause or causes of breast cancer remain unknown. Yet scientists have identified a number of risk factors that increase a person's chance of getting this disease. Certain risk factors, such as age, are beyond our control; whereas others, like drinking habits, can be modified.

Age

The risk of breast cancer increases with age. For example, annual breast cancer rates are 8-fold higher in women who are 50 years old, in comparison with women who are 30. Most breast cancers (about 80%) develop in women over the age of 50. In one age group (40 to 45 years), breast cancer is ranked first among all causes of death in women. Breast cancer is uncommon in women younger than 35, with the exception of those who have a family history of the disease.

Previous Breast Cancer

If a woman has already had breast cancer, she has a greater chance of developing a new cancer in the other breast. Such a new, or 'second,' cancer arises from a completely different location and should not be confused with a cancer that has recurred (come back) or metastasized (spread) from another site. The likelihood of a new cancer increases by 0.5% to 0.7% each year after the original diagnosis. After 20 years, a woman has a 10% to 15% chance of developing a new breast cancer.

A previous diagnosis of lobular carcinoma in situ (a localized tumor) is associated with a 10% to 30% greater breast cancer risk, and a previous diagnosis of ductal carcinoma in situ is associated with a 30% to 50% greater risk.

Family History Of Breast Cancer

Approximately 85% of women with breast cancer do NOT report a history of breast cancer within their families. Of the remaining 15%, about one-third appear to have a genetic abnormality. The risk of breast cancer is about two times higher among women who have a first-degree relative (mother, sister, or daughter) with this disease. The risk is increased 4- to 5-fold if the relative's cancer was found before menopause (the end of menstruation) and involved both breasts. The risk also is increased if breast cancer occurs in several family generations.

In addition, an increased risk of breast cancer has been found in families with other inherited disorders, such as ataxia telangiectasia (a progressive disease of the motor system) and Li-Fraumeni syndrome.

Genetic Mutations

About 5% to 10% of all breast cancers are hereditary. Scientists have identified certain genetic mutations (permanent changes in genetic material) that place people at increased risk of breast cancer. To date, the genes that have been most studied include BRCA1 and BRCA2. Some American women - many of whom are descendants of Ashkenazi Jews from Eastern and Central Europe - have an inherited BRCA1 mutation. Each will have up to a 90% lifetime risk of developing breast cancer. More than half will be diagnosed with breast cancer by age 50. In some BRCA1 families, there is a likelihood of developing both breast and ovarian cancers. The BRCA2 genetic mutation also is prevalent among families with Ashkenazi backgrounds.

In addition, many other genes may be associated with breast cancer, including the genes named p53, AT, the GADD repair group, the RB suppressor gene, and the HER-2/neu oncogene (a gene that contributes to cancer). Some of these genes directly influence breast cancer risk, whereas others are involved in the general processes of cancer growth and metastasis.

Hormones

Breast cancer risk is increased in women with the longest known exposures to sex hormones, particularly estrogen (female sex hormone). Therefore, breast cancer risk is increased in women who have a history of

• early first menstrual period (before age 12),
• late menopause (end of menstruation),
• no pregnancies,
• late pregnancy (after age 30), or use of
• birth control pills (the 'Pill;' oral contraceptives - 'OCs').

It should be mentioned that the Pill's exact hazards are difficult to assess, since risk apparently disappears in women who have not used oral contraceptives for more than 10 years.

Estrogen replacement therapy (ERT), also known as hormone replacement therapy (HRT), is used by many older women to relieve the symptoms of menopause. Certain studies indicate that ERT may increase the risk of breast cancer after long-term use (10+ years). Yet there is no official consensus on ERT, because scientists also have found that the increase in breast cancer risk is eliminated within 5 years of stopping ERT. In addition, some researchers have reported an increased risk of breast cancer in women taking estrogen or estrogen plus progestin, whereas others have not. Because of these uncertainties - and the fact that ERT has a number of positive benefits (e.g., lowered risks of bone fractures and heart attack) - a physician should be consulted about risks and benefits before a person uses ERT.