Breast cancer is a disease in which malignant (cancer) cells form in the tissues of the breast. Different factors increase or decrease the risk of breast cancer. Breast cancer is the second leading cause of death from cancer in American women. Women in the United States get breast cancer more than any other type of cancer except for skin cancer. Breast cancer is more likely to occur as a woman ages. It occurs more often in white women than in black women, but black women die from breast cancer more often than white women.
What is breast cancer screening?
Screening is looking for signs of disease before a person presents with symptoms. The goal of screening tests is to find cancer at an early stage when it can be treated and may be cured. Sometimes a screening test finds cancer that is very small or very slow growing. These cancers are unlikely to cause death or illness during the person’s lifetime. The primary goal of breast cancer screening is to reduce subsequent breast cancer mortality through early detection.
Who should screen?
Doctors look at the person’s age, their family history, and certain exposures during their lifetime. This information helps doctors recommend who should be screened for cancer, which screening tests should be used, and how often the tests should be done.
If the results from a screening test are abnormal, you may need to have further testing done to find out if you have cancer. These are called diagnostic tests, rather than screening tests.
How best to screen for breast cancer
There are a few different methods to use to screen for breast cancer. The largest study reported on 1,909 women at increased risk in the Netherlands, was with 45 women diagnosed with cancer who had all screening examinations. The sensitivity of clinical breast examination, mammography, and MRI in this study was 17.9%, 40%, and 71%, respectively.
Mammography is the most common screening test for breast cancer. A mammogram is an x-ray picture of the breast. Mammography may find tumors that are too small to feel. Mammography is less likely to find breast tumors in women with dense breast tissue. Because both tumors and dense breast tissue appear white on a mammogram, it can be harder to find a tumor when there is dense breast tissue. Younger women are more likely to have dense breast tissue. Women aged 50 to 69 years who have screening mammograms have a lower chance of dying from breast cancer than women who do not have screening mammograms.
Many factors affect whether mammography is able to detect breast cancer. These include:
- Age and weight of the patient
- Size and type of tumor
- Location of the tumor
- How sensitive the breast tissue is to hormones
- How dense the breast tissue is
- Timing of the mammography within the woman’s menstrual cycle
- Quality of the mammogram picture
- Skill of the radiologist in reading the mammogram
Women should be informed about the potential benefits (reduced chance of dying from breast cancer), potential harms (false-positive results, unnecessary biopsies), and limitations of the test that apply to women their age. The balance of benefits and potential harms of mammography improves with increasing age for women ages 40 to 70 years.
Magnetic resonance imaging (MRI)
MRI may be used to screen women who have a high risk of breast cancer. MRI is a procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body. MRI does not use any x-rays and the woman is not exposed to radiation. An MRI is more likely than mammography to find a breast mass that is not cancer. In addition, the high cost and low specificity of this test also need to be considered.
Factors that put women at high risk include certain gene changes, such as changes in the BRCA1 or BRCA2 genes, a family history (first-degree relative, such as a mother, daughter or sister) of breast cancer, and certain genetic syndromes, such as Li-Fraumeni or Cowden syndrome.
Breast examination is appealing as a patient-centered, noninvasive procedure that allows women to become comfortable with their own bodies. However, the extent of current practice is thought to be low. While associated with increased accuracy of detection of lumps in breast tissue, examination has been associated with increased rates of false-positive findings as well as increased biopsies.
The bottom line
Mammography remains the main breast cancer screening tool while the effectiveness of clinical breast examination and self-examination are less. New screening modalities are unlikely to replace mammography in the near future as the main tool for screening for breast cancer. There is good evidence that mammography screening every 12 to 33 months significantly reduces mortality from breast cancer. Evidence is strongest for women ages 50 to 69 years. Fewer women are dying of breast cancer in the United States, but it is not known whether the lower risk of dying is because the cancer was found early by screening or because better treatments are now available.
Written by Joanne Myers