Screening can be done in a variety of ways. X-ray mammography, which is most common, uses x-rays to scan breast tissue to detect cancers, which appear distinct from the surrounding tissue. Scanning of breast tissue can also be done with magnetic resonance imaging. Other methods are clinical breast exams, in which a health-care provider checks for abnormalities in the patient's breasts, and breast self-exams, in which the patient checks their own breasts for any abnormal lumps. These lumps may be cancerous, and once found can be separately tested. Finally, genetic testing for the BRCA1 and BRCA2 genes, which are tied to increased levels of breast cancer, is possible; this is generally only recommended for women with a family history with a particularly high rate of breast cancer.
Mammography is still the modality of choice for screening of early breast cancer, since it is relatively fast, reasonably accurate, and widely available in developed countries. Breast cancers detected by mammography are usually much smaller (earlier stage) than those detected by patients or doctors as a breast lump.
Due to the high incidence of breast cancer among older women, screening is now recommended in many countries. Recommended screening methods include breast self-examination and mammography. Mammography has been estimated to reduce breast cancer-related mortality by 20-30%. Routine (annual) mammography of women older than age 40 or 50 is recommended by numerous organizations as a screening method to diagnose early breast cancer and has demonstrated a protective effect in multiple clinical trials. The evidence in favor of mammographic screening comes from eight randomized clinical trials from the 1960s through 1980s. Many of these trials have been criticised for methodological errors, and the results were summarized in a review article published in 1993.
Improvements in mortality due to screening are hard to measure; similar difficulty exists in measuring the impact of Pap smear testing on cervical cancer, though worldwide, the impact of that test is likely enormous. Nationwide mortality due to cancer before and after the institution of a screening test is a surrogate indicator about the effectiveness of screening, and results of mammography are favorable.
The U.S. National Cancer Institute recommends screening mammography every one to two years beginning at age 40. In the UK, women are invited for screening once every three years beginning at age 50. Women with one or more first-degree relatives (mother, sister, daughter) with premenopausal breast cancer should begin screening at an earlier age. It is usually suggested to start screening at an age that is 10 years less than the age at which the relative was diagnosed with breast cancer.
A clinical practice guideline by the US Preventive Services Task Force recommended "screening mammography, with or without clinical breast examination (CBE), every 1 to 2 years for women aged 40 and older." The Task Force gave a grade B recommendation.
In 2005, 67.9% of all U.S. women age 40–64 had a mammogram in the past two years (74.5% of women with private health insurance, 56.1% of women with Medicaid insurance, 38.1% of currently uninsured women, and 32.9% of women uninsured for > 12 months). All U.S. states (except Utah) mandate that private health insurance plans and Medicaid provide some coverage for breast cancer screening. Section 4101 of the Balanced Budget Act of 1997 required that Medicare (available to those aged 65 or older or who have been on Social Security Disability Insurance for over 2 years), effective January 1, 1998, cover and waive the Part B deductible for annual screening mammography in women aged 40 or older.
All organized breast cancer screening programs in Canada offer clinical breast examinations for women aged 40 and over and screening mammography every two years for women aged 50-69. In 2003, about 61% of women aged 50-69 in Canada reported having had a mammogram within the past two years.
The NHS Breast Screening Programme, the first of its kind in the world, began in 1988 and achieved national coverage in the mid-1990s, provides free breast cancer screening mammography every three years for all women in the UK aged 50 and over. As of March 31, 2006, 75.9% of women aged 53-64 resident in England had been screened at least once in the previous three years.
False positives are a major problem of mammographic breast cancer screening. Data reported in the UK Million Woman Study indicates that if 134 mammograms are performed, 20 women will be called back for suspicious findings, and four biopsies will be necessary, to diagnose one cancer. Recall rates are higher in the U.S. than in the UK. The contribution of mammography to the early diagnosis of cancer is controversial, and for those found with benign lesions, mammography can create a high psychological and financial cost.
A systematic review by the American College of Physicians concluded "Although few women 50 years of age or older have risks from mammography that outweigh the benefits, the evidence suggests that more women 40 to 49 years of age have such risks".
Computer-aided diagnosis(CAD) Systems may help radiologists to evaluate X-ray images to detect breast cancer in an early stage. CAD is especially established in US and the Netherlands. It is used in addition to the human evaluation of the diagnostician.
However, two studies published in 2007 demonstrated the strengths of MRI-based screening:
Breast self-examination was widely discussed in the 1990s as a useful modality for detecting breast cancer at an earlier stage of presentation. A large clinical trial in China reduced enthusiasm for breast self-exam. In the trial, reported in the Journal of the National Cancer Institute first in 1997 and updated in 2002, 132,979 female Chinese factory workers were taught by nurses at their factories to perform monthly breast self-exam, while 133,085 other workers were not taught self-exam. The women taught self-exam tended to detect more breast nodules, but their breast cancer mortality rate was no different from that of women in the control group. In other words, women taught breast self-exam were mostly likely to detect benign breast disease, but were just as likely to die of breast cancer. An editorial in the Journal of the National Cancer Institute reported in 2002, "Routinely Teaching Breast Self-Examination is Dead. What Does This Mean?"
The Task Force noted that about 2% of women have family histories that indicate increased risk as defined by: