Despite its demonstrated ability to detect breast cancer early and reduce disease-specific mortality rates to some degree, mammography has inherent limitations and risks like any cancer screening technology (including physical examination). Because the sensitivity and specificity are not 100 percent, screening programs will necessarily produce some false findings, both false-positive and false-negative findings, which can have detrimental effects on the screened population. Furthermore, identification of breast cancer by screening mammography does not guarantee that a woman will not die of breast cancer. Even small tumors may develop the ability to metastasize, and in these cases, early detection and treatment will not necessarily produce a cure. Some cancers will also rapidly develop during the period between screenings (termed interval cancers), and such aggressive tumors may not be amenable to treatment.
One limitation with the current technology for mammography is the high rate of false-positive results, which are abnormal findings in patients who are subsequently found to be free of breast cancer. To avoid large numbers of false-positive results, the specificity of a test must reach 99 percent or more, but most screening tests for cancer have much lower specificities. For published reports on mammography, specificities generally fall in the range of 90 to 98 percent (Mushlin et al., 1998). The risk of having a false-positive result by mammography during routine yearly screening may be as high as 10 percent (Brown et al., 1995). One study suggests that among women who receive annual mammograms for 10 years, half will have at least one false-positive result that leads to additional tests such as diagnostic mammography, ultrasound, or biopsy (Christiansen et al., 2000; Elmore et al., 1998a). Currently, as many as three-fourths of all biopsy specimens turn out to be benign lesions. As acceptance and use of mammographic screening become more widespread, the increasing number of false-positive results becomes a cause for concern.
Short-term studies have shown that abnormal mammograms negatively affect a woman’s psychological and emotional state (Lowe et al., 1999). Even when further evaluation rules out cancer, some women report impaired moods and daily functioning for up to 3 months after a suspicious finding on a mammogram (Lerman et al., 1991). A study in Norway examined perceptions of quality of life 18 months following a false-positive mammogram. Most women in that study regard their experience with a false-positive mammogram as one of the many minor stressful life incidences, with only a temporary decrease in quality of life (Gram et al., 1990). However, women with false-positive mammograms also experience heightened levels of concern about breast cancer (Lowe et al., 1999; Gram et al., 1990). Previously, it was commonly believed that fear could prevent women from returning for a second screening following a false-positive result. However, a recent study showed that women with false-positive mammograms, especially those who had no previous mammograms, were actually more likely to come in for their next scheduled visit (Burman et al., 1999; Pisano et al., 1998a).
The medical procedures that are necessary after a suspicious mammogram have additional consequences, both physical and financial. Follow-up work to an initial screening test can include diagnostic mammograms, ultrasound examinations, and needle or surgical biopsies. Pain and reduced sexual sensitivity due to surgical biopsy are possible side effects (Gram et al., 1990). Lost productivity as a result of time off for surgery and recuperation is an additional cost. Retrospective studies show that the additional costs of evaluating false-positive results can add up to one-third of the total cost of screening for all women (Elmore et al., 1998a; Lidbrink et al., 1996). Furthermore, scarring of the tissue following surgical biopsy may result in cosmetic concerns and could potentially interfere with subsequent cancer detection. However, improvements in biopsy techniques have led to smaller and less invasive procedures and have thus reduced some of these concerns.
No screening or diagnostic technology is perfect, and thus, some false-negative results are inevitable. A normal mammogram does not guarantee that a woman is free of breast cancer because some tumors are not detected by mammography. The sensitivity of screening mammography (ability to detect occult cancer) ranges from 83 to 95 percent in published studies (Mushlin et al., 1998). Failure to detect breast cancer can generally be attributed to one of four main reasons: inherent limitations of mammography, inadequate radiographic technique, subtle or unusual lesion characteristics, and errors of interpretation. A number of studies have shown that a significant portion of breast cancers detected at follow-up mammography are visible in retrospect on the previous mammogram that was interpreted as normal (Harvey et al., 1993; van Dijck et al., 1993; Warren Burhenne et al., 2000). Regardless of the cause, a false-negative finding on a mammogram can be quite harmful to the woman whose cancer has been missed. Normal findings on a mammogram may produce a false sense of security that could prevent women from seeking appropriate medical attention, even for symptomatic lesions. A delay in diagnosis will delay treatment, perhaps in some cases to the point where treatment will no longer be effective because the tumor has had sufficient time to progress and metastasize. Because of these potential dire consequences associated with false-negative findings, the number of medical malpractice lawsuits stemming from missed cancer diagnoses has increased considerably since screening programs were widely introduced.
In fact, a recent report suggests that lawsuits alleging a missed or delayed breast cancer diagnosis are now the most prevalent of all medical malpractice suits filed against radiologists and physicians in general (Berlin, 1999; Physicians Insurers Association of America, 1995, 1997).