Each month, The Clinical Advisor makes one new clinical feature available ahead of print. Don’t forget to take the poll. The results will be published in the next month’s issue.
Mammography is one of the most studied screening tests in medicine; since the advent of screening mammography, the rate of breast cancer mortality has decreased by more than 30% in the United States.1 Moreover, numerous studies have corroborated that conventional mammography is the only effective population-based strategy for early detection that mitigates the risk for breast cancer–specific mortality.2,3
Surprisingly, there is no consensus among current medical communities regarding how frequently mammography should be done or the age at which it should begin. Significant debate exists about whether the benefits of mammography outweigh the potential negative effects, about what constitutes harm, and about where a benefit-harm threshold may lie, and the outcomes of research on these issues have been inconclusive. In the current review, we analyze mammography screening guidelines from US organizations to understand best practices in an effort to minimize the morbidity and mortality of breast cancer.
Breast cancer epidemiology
Worldwide, breast cancer remains the most frequent cause of cancer-related death in women.4-7 A woman’s probability of developing breast cancer changes with age,8-10 and mortality rates often reflect differences in ethnicity and geographic location. In the United States, for example, the incidence of breast cancer is highest in white and African American women, yet the rates of breast cancer mortality are higher in African American women.9,11
The international incidence of breast cancer also varies considerably; rates are higher in Western Europe and North America and lower in Asia and sub-Saharan Africa.12,13 Fortunately, breast cancer mortality has decreased in several European countries during the past 25 years, primarily because of early detection via mammography and improved treatment.13-16 Interestingly, studies of Japanese, Chinese, and Korean persons who have immigrated to the United States indicate a progressive increase in breast cancer risk in successive generations, suggesting that behavioral factors in the previous cultures may have conferred a protective effect against the disease.17
Risk factors for the development of breast cancer also vary and can be related to family history, genetic alterations, race, age, nulliparity, menstrual history, and breast density. Additionally, hormone use, diethylstilbestrol use, alcohol consumption, physical inactivity, radiation therapy, and increased body weight are recognized and modifiable risk factors for breast cancer.18
In a consideration of the data on mammography screening, it is essential to understand the widely disparate views and recognize the limitations of the data on which conclusions are based. For example, the results of randomized controlled trials (RCTs) on screening mammography may be adversely affected by noncompliance and study group contamination to a greater degree than the results of other types of RCTs, especially pharmaceutical trials. Noncompliance is the failure of a subject in the intervention group to undergo mammographic screening as directed; contamination occurs when a study participant in the control group undergoes screening outside the study protocol. The effects of noncompliance and contamination effectively dilute the performance of mammography screening and effectuate an underestimation of the measure’s true benefit.19