Screening for Breast Cancer

What is screening?

Screening for cancer is examination (or testing) of people for early stages in the development of cancer even though they have no symptoms. Scientists have studied patterns of cancer in the population to learn which people are more likely to get certain types of cancer. They have also studied what things around us and what things we do in our lives may cause cancer. This information sometimes helps doctors recommend who should be screened for certain types of cancer, what types of screening tests people should have, and how often these tests should be done. Not all screening tests are helpful, and they often have risks. For this reason, scientists at the National Cancer Institute are studying many screening tests to find out how useful they are and to determine the relative benefits and harms.

If your doctor suggests certain cancer screening tests as part of your health care plan, this does not mean he or she thinks you have cancer. Screening tests are done when you have no symptoms. Since decisions about screening can be difficult, you may want to discuss them with your doctor and ask questions about the potential benefits and risks of screening tests and whether they have been proven to decrease the risk of dying from cancer.

If your doctor suspects that you may have cancer, he or she will order certain tests to see whether you do. These are called diagnostic tests. Some tests are used for diagnostic purposes, but are not suitable for screening people who have no symptoms.

Purposes of this summary

The purposes of this summary on breast cancer screening are to:

• give information on breast cancer and what makes it more likely to occur (risk factors)
• describe breast cancer screening methods and what is known about their effectiveness

You can talk to your doctor or health care professional about cancer screening and whether it would be likely to help you.

Breast Cancer Screening

The breast consists of lobes, lobules, and bulbs that are connected by ducts. The breast also contains blood and lymph vessels. These lymph vessels lead to structures that are called lymph nodes. Clusters of lymph nodes are found under the arm, above the collarbone, in the chest, and in other parts of the body. Together, the lymph vessels and lymph nodes make up the lymphatic system, which circulates a fluid called lymph throughout the body. Lymph contains cells that help fight infection and disease.

When breast cancer spreads outside the breast, cancer cells are most often found under the arm in the lymph nodes. In many cases, if the cancer has reached the lymph nodes, cancer cells may have also spread to other parts of the body via the lymphatic system or through the bloodstream.

Risk of breast cancer

More women in the United States get breast cancer than any other type of cancer (except for skin cancer). The number of cases per 1,000 women has increased slightly every year over the last 50 years. It is the second leading cause of death from cancer in women (lung cancer causes the most deaths from cancer in women). Breast cancer occurs in men also, but the number of new cases is small.

Anything that increases a person's chance of developing a disease is called a risk factor. Some of these risk factors for breast cancer are as follows:

Age - Breast cancer is more likely to develop as you grow older. Beginning menstruation at an early age and late age at first birth may also increase the risk of development of breast cancer.

History of Breast Cancer - If you have already had breast cancer, you are more likely to develop breast cancer again.

Family History - If your mother or sister had breast cancer, you are more likely to develop breast cancer, especially if they had it at an early age.

Radiation Therapy - Radiation therapy to the chest that was given more than 10 years ago, especially in women younger than 30 years old, may increase a woman's risk of developing breast cancer.

Other Breast Diseases - If you have had a breast biopsy specimen that showed certain types of benign breast conditions, you may be more likely to develop breast cancer. For most women, however, the ordinary "lumpiness" they feel in their breasts does not increase their risk of breast cancer.

Studies have found that race, social status, income, education, and access to screening and treatment services may affect a woman's risk of developing breast cancer.

Screening tests for breast cancer

Breast Self-Examination - When you examine your own breasts it is called breast self-examination (BSE). Studies so far have not shown that BSE alone reduces the number of deaths from breast cancer. Therefore, it should not be used in place of clinical breast examination and mammography.

Clinical Breast Examination - During your routine physical examination, your doctor or health care professional may do a clinical breast examination (CBE). During a CBE, your doctor will carefully feel your breasts and under your arms to check for lumps or other unusual changes.

Mammogram - A mammogram is a special x-ray of the breast that can often find tumors that are too small for you or your doctor to feel. Your doctor may suggest that you have a mammogram, especially if you have any of the risk factors listed above.

The ability of mammography to detect cancer depends on such factors as the size of the tumor, the age of the woman, breast density, and the skill of the radiologist. Studies have found that screening mammography is beneficial in women aged 50 to 69. Screening in women younger than 50 years or older than 69 years may or may not be helpful.

Ultrasonography - During ultrasonography, sound waves (called ultrasound) are bounced off tissues and the echoes are converted into a picture (sonogram). Ultrasound is used to evaluate lumps that have been identified by BSE, CBE, or mammography. Studies have not shown that ultrasonography is of any proven benefit in detecting breast cancer.

Magnetic Resonance Imaging (MRI) - A procedure in which a magnet linked to a computer is used to create detailed pictures of areas inside the body. MRIs are used to evaluate breast masses that have been found by BSE or CBE and to recognize the difference between cancer and scar tissue. The role of MRI in breast cancer screening has not yet been established.

Other screening methods are being studied. Your doctor can talk to you about what screening tests would be best for you.

Source: National Cancer Institute, National Institutes of Health, November 2000