A mammogram is an X-rayexamination of the breast, performed for screening or diagnostic purposes. A screening mammogram is used to detect breast cancer before it is clinically apparent. Two views of the breast tissue are taken: a mediolateral (MLO) view and a craniocaudal (CC) view. A diagnostic mammogram is utilized to evaluate abnormalities seen on a screening mammogram or to further characterize abnormalities on physical examination.
Screening mammography has been shown to decrease breast cancer mortality, particularly for women 40 to 50 years of age and older. The first randomized, controlled trial to evaluate the benefit of mammogram and clinical breast-exam screening was the HIP (Health Insurance Plan) study, initiated in 1963. Approximately 62,000 women between 40 and 64 years of age were assigned at random to either a mammography and clinical breast exam group for four years or to a control group. After ten years of follow-up, the study group had a 30 percent lower mortality from breast cancer in comparison to the control group.
Further randomized controlled trials confirmed the efficacy of screening mammography in decreasing breast cancer mortality. A meta-analysis of nine randomized controlled trials and four case-control studies was reported in 1995. Women aged 50 to 74 who received mammographic screening had a decreased relative risk for breast cancer mortality of 0.74 (95% CI [confidence interval],0.66–0.83) in comparison to women who did not receive mammographic screening. No reduction in breast cancer mortality with mammographic screening was seen in women aged 40 to 49, after 7 to 9 years of follow-up. With a longer duration of follow-up of 10 to 12 years, there was a 17 percent decrease in breast cancer mortality among women aged 40 to 49 who received screening mammography.
A meta-analyses of eight randomized trials of screening mammography in women aged 40 to 49 was published in 1997. This meta-analysis demonstrated an 18 percent mortality reduction in women aged 40 to 49 who received screening mammography, after 10.5 to 18 years of follow-up.
Based on these results, it is clear that women 50 years old and older benefit from yearly screening mammography in order to decrease their risk of dying from breast cancer; however, there is controversy regarding the utility of screening mammography in women aged 40 to 49. An attempt at resolving this controversy was made at the National Institute of Health Consensus meeting in January 1997, but a consensus could not be reached. Therefore the meeting resulted in two different reports regarding screening mammography in women aged 40 to 49. The majority concluded that screening mammogram was not universally warranted in this age group. A minority report, however, supported the recommendation for screening mammography based on the survival benefit seen at 10 years and longer after screening is initiated. The American Cancer Society supports this recommendation, recommending an annual mammogram for women aged 40 and older.
Another area of controversy is the upper age limit at which to stop performing screening mammography. There is no data from randomized trials regarding the benefits of screening mammography in women older than 75 because of the lack of enrollment of elderly women. This area deserves further study, given that age is the single greatest risk factor for breast cancer and approximately half of all breast cancers occur in women over the age of 65. The American Cancer Society and the National Cancer Institute put no upper age cut-off for screening mammography. The American Geriatric Society has published a position statement regarding breast cancer screening in older women, recommending no upper age limit for breast cancer screening for women with an estimated life expectancy of greater than four years (2000).
Ultimately, the decision regarding screening mammography is up to the patient. Therefore, it is important for a clinician to discuss the benefits and risks of mammographic screening with each individual. The risks of mammographic screening include the risk of a false positive exam, which can lead to further testing, cost, and patient anxiety. Younger women have a higher rate of false positive and false negative exams, a consequence of the exam being less sensitive and specific in this age group. In addition, there is an exceedingly small risk of breast cancer due to radiation exposure from the mammogram. Statistical models indicate that 8 out of 100,000 women who underwent an annual mammogram for 10 years beginning at age 40 develop breast cancer and die from the disease during their lifetime. Women with DNA repair mechanism impairment may be at greater risk.