The key to finding breast cancer is early detection, and the key to early detection is screening: looking for cancer in women who have no symptoms of disease. The best available tool is a regular screening mammogram--x-ray of the breast--coupled with a clinical breast exam--by a doctor or nurse.

Mammography A mammogram is an x-ray of the breast. Cancers that are found
on mammograms but that cannot be felt (nonpalpable cancers) usually are smaller than cancers that can be felt, and they are less likely to have spread.

Mammography is not foolproof. Some breast changes, including lumps that can be felt, do not show up on a mammogram. Changes can be especially difficult to spot in the dense, glandular breasts of younger women. This is why women of all ages should have their breasts examined every year by a physician or trained health professional.

~ A lump should never be ignored just
because it is not visible on a mammogram.~

Two Kinds of Mammography: Diagnostic and Screening
If a woman visits her doctor because of unusual breast changes such as a lump, pain, nipple thickening or discharge, or changes in breast size or shape, or has a suspicious screening mammogram, the doctor often asks her to have a diagnostic mammogram: an x-ray of the breast to help assess her symptoms. A diagnostic mammogram is a basic medical tool, and it is appropriate for women of any age.

This booklet discusses screening mammograms: x-rays that are used to look for breast changes in women who have no signs of breast cancer. (Even though the woman has no symptoms of breast disease, a diagnosis of breast cancer can begin with a doctor checking a screening mammogram.)

What Are the Benefits of Screening Mammography?
High-quality mammography is the most effective tool now available to detect breast cancer early, before symptoms appear--often before a breast lump can even be felt. Regularly scheduled mammograms can decrease a woman's chance of dying from breast cancer. For some women, early detection may prevent the need to remove the entire breast or receive chemotherapy.

Who Benefits From Screening Mammography?
Studies done over the past 30 years clearly show that regular screening mammography significantly reduces the death rate from breast cancer in women over the age of 50. Recent results from studies show that regular mammography also reduces death rates from breast cancer in women who begin screening in their forties.

The effectiveness of mammography seems to increase as a woman ages, and the time it takes for benefits to emerge appears to take longer in younger women.

Who Is at Average Risk for Breast Cancer?
Simply being a woman and getting older puts you at average risk for developing breast cancer. The older you are, the greater your chance of getting breast cancer. No woman should consider herself too old to need regular screening mammograms.

Who Is at Higher Than Average Risk for Breast Cancer?
One or more of the following conditions place a woman at higher than average risk for breast cancer:

• personal history of a prior breast cancer
  
• evidence of a specific genetic change that increases susceptibility to breast cancer (See Gene Testing for Breast Cancer Susceptibility, page 18.)
  
• mother, sister, daughter, or two or more close relatives, such as cousins, with a history of breast cancer (especially if diagnosed at a young age)
  
• a diagnosis of a breast condition that may predispose a woman to breast cancer (i.e., atypical hyperplasia), or a history of two or more breast biopsies for benign breast disease (See Benign Breast Conditions and the Risk for Breast Cancer, page 26.)

Also playing a role in a heightened risk for breast cancer is breast density. Women ages 45 or older who have at least 75 percent dense tissue on a mammogram are at elevated risk. And a slight increase in the risk of breast cancer is associated with having a first birth at age 30 or older.

In addition, women who receive chest irradiation for conditions such as Hodgkin's disease at age 30 or younger remain at higher risk for breast cancer throughout their lives. These women require meticulous surveillance for breast cancer.

These factors that increase cancer risk--risk factors--do not by themselves cause cancer. Having one or more does not mean that you are certain or even likely to develop breast cancer. Even among women with no other risk factors except a strong family history--for example, both a mother and a sister or two sisters with early onset breast cancer--three-fourths will not develop the disease.

Clearly, there is much yet to be learned about what causes breast cancer.

~ On the other hand, not having any of the known risk factors
does not mean that you are "safe." Most women who develop
breast cancer do not have a strong family history of breast
cancer or fall into any special higher risk category. ~

What Are the Limitations of Screening Mammography?
Early detection by mammography does not guarantee that a woman's life will be saved. It may not help a woman who has a fast-growing cancer that has spread to other parts of her body before being detected. Also, about half of the women whose breast cancers are detected by mammography would not have died from cancer, even if they had waited until the lump could be felt, because their tumors are slow-growing and treatable.

False Negative Mammograms
Breasts of younger women contain many glands and ligaments. Because their breasts appear dense on mammograms, it is difficult to see tumors or to distinguish between normal and abnormal breast conditions. As a woman grows older, the glandular and fibrous tissues of her breasts gradually give way to less dense fatty tissues. Mammograms can then see into the breast tissue more easily to detect abnormal changes. About 25 percent of breast tumors are missed in women in their forties, compared to about 10 percent of women older than age 50. These are called false negatives. A normal mammogram in a woman with symptoms does not rule out breast cancer. Sometimes a clinical breast exam by a doctor or nurse can reveal a breast lump that is missed by a mammogram.

False Positive Mammograms
Between 5 and 10 percent of mammogram results are abnormal and require more testing (more mammograms, fine needle aspiration, ultrasound, or biopsy), and most of the followup tests confirm that no cancer was present. It is estimated that a woman who has yearly mammograms between ages 40 and 49 would have about a 30 percent chance of having a false positive mammogram at some point in that decade, and about a 7 to 8 percent chance of having a breast biopsy within the 10-year period. The estimate for false positive mammograms is about 25 percent for women ages 50 or older.

Increased Cases of Ductal Carcinoma In Situ (DCIS)
The increased use of screening mammography has increased the detection of small abnormal tissue growths confined to the milk ducts in the breast, called ductal carcinoma in situ (DCIS). Doctors don't know which, if any, cases of DCIS may become life threatening. Usually, the growth is removed surgically, and radiation treatment is often given.

How Mammograms Are Made Mammography is a simple procedure. It uses a "dedicated" x-ray machine specifically designed for x-raying the breast and used only for that purpose (in contrast to machines used to take x-rays of the bones or other parts of the body). The standard screening exam includes two views of each breast, one from above and one angled from the side. A registered technologist places the breast between two flat plastic plates. The two plates are then pressed together. The idea is to flatten the breast as much as possible; spreading the tissue out makes any abnormal details easier to spot with a minimum of radiation. The technologist takes the x-ray, then repeats the procedure for the
next view.

The pressure from the plates may be uncomfortable, or even somewhat painful. It helps to remember that each x-ray takes less than one minute--and it could save your life. It also helps to schedule mammography just after your period, when your breasts are least likely to be tender, or at the same time each year, if you no longer have your period.

Although some women are concerned about radiation exposure, the risk of any harm is extremely small. The doses of radiation used for mammography are very low and considered safe. The exact amount of radiation needed for a specific mammogram will depend on several factors. For instance, breasts that are large or dense will require higher doses to get a clear image. Federal mammography guidelines limit the radiation used for each exposure of the breast to 0.3 rad. (A "rad" is a unit of measurement that stands for radiation absorbed dose.) In practice, most mammograms deliver just a small fraction of this amount.

Specialized mammography facilities have experienced personnel as well as modern equipment that is custom designed for mammograms. The combination of good technology and expertise makes it possible to obtain good-quality x-ray images with very low doses of radiation.

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