Info

Not reported

The first study to test mammography and have surgeons operate based on nonpalpable lesions.

Used community radiologists; all women screened by CBE at baseline.

Used community radiologists; all women screened by CBE at baseline.

Randomization by physician practice resulted in population differences. Recent metaanalyses exclude this study.

Most commonly cited study. Used 2-year interval for women 40-49 and 3-year interval for women 50-74.

breast cancer mortality over 14 years of follow-up among women aged 40 to 49 years and 22% breast cancer mortality reduction over 14 years among women ages 50 to 74.7 Although the difference in cumulative mortality appears to increase with follow-up among intervention women ages 40 to 49 compared with controls, the benefit decreases with time among women ages 50 to 74.7 Some have suggested that screening may actually result in higher breast cancer mortality based on the cumulative mortality for the first 3 to 4 years among intervention women compared with control women.4 Whether that difference is real or not, it disappears with time. Because film-screen mammography technology has improved since the randomized trials began, some groups believe that the benefit is greater for those seeking screening today.54

Despite the consensus in the United States to begin screening at age 40, there is some controversy about the findings on which this recommendation is based.4,5,55,56 In all randomized trials, the number of cancers found within a particular age group is relatively small, so there are advantages to combining results from several trials. However, each trial has unique characteristics and was implemented by different teams. Most of the controversy has to do with the internal validity of the trials and whether their results can be combined to provide an overall estimate of film-screen mam-mography's impact7,27

Two investigators, Olsen and Gotzsche, reviewed eight trials and raised questions about randomization, comparability of the cases and controls, assessment of cause of death, and exclusions after randomization.55 These investigators concluded that only two trials met standards of research quality that justify inclusion in meta-analysis; neither trial showed a benefit. The USPSTF reviewed the same list of trials and kept all but one in its analysis.7 A separate meta-analysis by an international group produced the same conclusion as the USPSTF regarding which trials to exclude from meta-analyses, and estimated a 19% mortality reduction at 14 years among women ages 40 to 49 and a 25% mortality reduction among women ages 50 to 69, but only the latter was statistically significant.27

Because of the controversies surrounding mammography, there is widespread agreement that the determination of whether to screen should be based on an informed decision that acknowledges that any benefit among populations of younger women is evident only after many years and that the overall benefit for all women is modest.4,5 Part of the informed decision-making process should include the information that one reason for the modest benefit is that many women diagnosed with breast cancer do well when detected in the course of usual care.57 To show a benefit, screening must perform better than usual care. Furthermore, because the effect on mortality is moderate, a high quality of screening implementation is important to reproduce the impact demonstrated in the trials.

There are persistent questions regarding the optimal frequency with which to screen, and there is no randomized trial comparing 1- versus 2-year screening intervals. There has been a trial to compare film-screen mammography intervals every 1 versus 3 years among women aged 50 to 62 years.58 In this trial, the investigators estimated expected deaths based on the observed stage differences between two screening groups and concluded there was no advantage to annual film-screen mammography compared to triennial screening.58

However, because the sojourn time for young women is close to 2 years, some argue that the screening interval for this age group should be 1 year.28,59

Recommendations

The ACS recommends annual film-screen mammography and clinical breast examination beginning at age 40.59 They recommend individualizing decisions about when to stop screening.

The USPSTF recommends screening film-screen mam-mography, with or without clinical breast examination, every 1 to 2 years for women aged 40 and older and also recognizes the need to individualize when to stop screening.7

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