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Background: The goal of screening mammography is to detect small malignant tumors before they grow large enough to cause symptoms. Effective screening should therefore lead to the detection of a greater number of small tumors, followed by fewer large tumors over time., Methods: We used data from the Surveillance, Epidemiology, and End Results (SEER) program, 1975 through 2012, to calculate the tumor-size distribution and size-specific incidence of breast cancer among women 40 years of age or older. We then calculated the size-specific cancer case fatality rate for two time periods: a baseline period before the implementation of widespread screening mammography (1975 through 1979) and a period encompassing the most recent years for which 10 years of follow-up data were available (2000 through 2002)., Results: After the advent of screening mammography, the proportion of detected breast tumors that were small (invasive tumors measuring <2 cm or in situ carcinomas) increased from 36% to 68%; the proportion of detected tumors that were large (invasive tumors measuring ≥2 cm) decreased from 64% to 32%. However, this trend was less the result of a substantial decrease in the incidence of large tumors (with 30 fewer cases of cancer observed per 100,000 women in the period after the advent of screening than in the period before screening) and more the result of a substantial increase in the detection of small tumors (with 162 more cases of cancer observed per 100,000 women). Assuming that the underlying disease burden was stable, only 30 of the 162 additional small tumors per 100,000 women that were diagnosed were expected to progress to become large, which implied that the remaining 132 cases of cancer per 100,000 women were overdiagnosed (i.e., cases of cancer were detected on screening that never would have led to clinical symptoms). The potential of screening to lower breast cancer mortality is reflected in the declining incidence of larger tumors. However, with respect to only these large tumors, the decline in the size-specific case fatality rate suggests that improved treatment was responsible for at least two thirds of the reduction in breast cancer mortality., Conclusions: Although the rate of detection of large tumors fell after the introduction of screening mammography, the more favorable size distribution was primarily the result of the additional detection of small tumors. Women were more likely to have breast cancer that was overdiagnosed than to have earlier detection of a tumor that was destined to become large. The reduction in breast cancer mortality after the implementation of screening mammography was predominantly the result of improved systemic therapy.

Importance: Screening mammography rates vary considerably by location in the United States, providing a natural opportunity to investigate the associations of screening with breast cancer incidence and mortality, which are subjects of debate., Objective: To examine the associations between rates of modern screening mammography and the incidence of breast cancer, mortality from breast cancer, and tumor size., Design, Setting, and Participants: An ecological study of 16 million women 40 years or older who resided in 547 counties reporting to the Surveillance, Epidemiology, and End Results cancer registries during the year 2000. Of these women, 53,207 were diagnosed with breast cancer that year and followed up for the next 10 years. The study covered the period January 1, 2000, to December 31, 2010, and the analysis was performed between April 2013 and March 2015., Exposures: Extent of screening in each county, assessed as the percentage of included women who received a screening mammogram in the prior 2 years., Main Outcomes and Measures: Breast cancer incidence in 2000 and incidence-based breast cancer mortality during the 10-year follow-up. Incidence and mortality were calculated for each county and age adjusted to the US population., Results: Across US counties, there was a positive correlation between the extent of screening and breast cancer incidence (weighted r = 0.54; P < .001) but not with breast cancer mortality (weighted r = 0.00; P = .98). An absolute increase of 10 percentage points in the extent of screening was accompanied by 16% more breast cancer diagnoses (relative rate [RR], 1.16; 95% CI, 1.13-1.19) but no significant change in breast cancer deaths (RR, 1.01; 95% CI, 0.96-1.06). In an analysis stratified by tumor size, we found that more screening was strongly associated with an increased incidence of small breast cancers (≤2 cm) but not with a decreased incidence of larger breast cancers (>2 cm). An increase of 10 percentage points in screening was associated with a 25% increase in the incidence of small breast cancers (RR, 1.25; 95% CI, 1.18-1.32) and a 7% increase in the incidence of larger breast cancers (RR, 1.07; 95% CI, 1.02-1.12)., Conclusions and Relevance: When analyzed at the county level, the clearest result of mammography screening is the diagnosis of additional small cancers. Furthermore, there is no concomitant decline in the detection of larger cancers, which might explain the absence of any significant difference in the overall rate of death from the disease. Together, these findings suggest widespread overdiagnosis.

Like all early detection strategies, screening mammography involves trade-offs. If women are to truly participate in the decision of whether or not to be screened, they need some quantification of its benefits and harms. Providing such information is a challenging task, however, given the uncertainty--and underlying professional disagreement--about the data. In this article, we attempt to bound this uncertainty by providing a range of estimates-optimistic and pessimistic--on the absolute frequency of 3 outcomes important to the mammography decision: breast cancer deaths avoided, false alarms, and overdiagnosis. Among 1000 US women aged 50 years who are screened annually for a decade, 0.3 to 3.2 will avoid a breast cancer death, 490 to 670 will have at least 1 false alarm, and 3 to 14 will be overdiagnosed and treated needlessly. We hope that these ranges help women to make a decision: either to feel comfortable about their decision to pursue screening or to feel equally comfortable about their decision not to pursue screening. For the remainder, we hope it helps start a conversation about where additional precision is most needed.

Background: To reduce mortality, screening must detect life-threatening disease at an earlier, more curable stage. Effective cancer-screening programs therefore both increase the incidence of cancer detected at an early stage and decrease the incidence of cancer presenting at a late stage., Methods: We used Surveillance, Epidemiology, and End Results data to examine trends from 1976 through 2008 in the incidence of early-stage breast cancer (ductal carcinoma in situ and localized disease) and late-stage breast cancer (regional and distant disease) among women 40 years of age or older., Results: The introduction of screening mammography in the United States has been associated with a doubling in the number of cases of early-stage breast cancer that are detected each year, from 112 to 234 cases per 100,000 women--an absolute increase of 122 cases per 100,000 women. Concomitantly, the rate at which women present with late-stage cancer has decreased by 8%, from 102 to 94 cases per 100,000 women--an absolute decrease of 8 cases per 100,000 women. With the assumption of a constant underlying disease burden, only 8 of the 122 additional early-stage cancers diagnosed were expected to progress to advanced disease. After excluding the transient excess incidence associated with hormone-replacement therapy and adjusting for trends in the incidence of breast cancer among women younger than 40 years of age, we estimated that breast cancer was overdiagnosed (i.e., tumors were detected on screening that would never have led to clinical symptoms) in 1.3 million U.S. women in the past 30 years. We estimated that in 2008, breast cancer was overdiagnosed in more than 70,000 women; this accounted for 31% of all breast cancers diagnosed., Conclusions: Despite substantial increases in the number of cases of early-stage breast cancer detected, screening mammography has only marginally reduced the rate at which women present with advanced cancer. Although it is not certain which women have been affected, the imbalance suggests that there is substantial overdiagnosis, accounting for nearly a third of all newly diagnosed breast cancers, and that screening is having, at best, only a small effect on the rate of death from breast cancer.

Background: Perhaps the most persuasive messages promoting screening mammography come from women who argue that the test "saved my life." Because other possibilities exist, we sought to determine how often lives were actually saved by mammography screening., Methods: We created a simple method to estimate the probability that a woman with screen-detected breast cancer has had her life saved because of screening. We used DevCan, the National Cancer Institute's software for analyzing Surveillance Epidemiology and End Results (SEER) data, to estimate the 10-year risk of diagnosis and the 20-year risk of death--a time horizon long enough to capture the downstream benefits of screening. Using a range of estimates on the ability of screening mammography to reduce breast cancer mortality (relative risk reduction [RRR], 5%-25%), we estimated the risk of dying from breast cancer in the presence and absence of mammography in women of various ages (ages 40, 50, 60, and 70 years)., Results: We found that for a 50-year-old woman, the estimated risk of having a screen-detected breast cancer in the next 10 years is 1910 per 100,000. Her observed 20-year risk of breast cancer death is 990 per 100,000. Assuming that mammography has already reduced this risk by 20%, the risk of death in the absence of screening would be 1240 per 100,000, which suggests that the mortality benefit accrued to 250 per 100,000. Thus, the probability that a woman with screen-detected breast cancer avoids a breast cancer death because of mammography is 13% (250/1910). This number falls to 3% if screening mammography reduces breast cancer mortality by 5%. Similar analyses of women of different ages all yield probability estimates below 25%., Conclusions: Most women with screen-detected breast cancer have not had their life saved by screening. They are instead either diagnosed early (with no effect on their mortality) or overdiagnosed.

Background: The introduction of screening mammography has been associated with sustained increases in breast cancer incidence. The natural history of these screen-detected cancers is not well understood., Methods: We compared cumulative breast cancer incidence in age-matched cohorts of women residing in 4 Norwegian counties before and after the initiation of biennial mammography. The screened group included all women who were invited for all 3 rounds of screening during the period 1996 through 2001 (age range in 1996, 50-64 years). The control group included all women who would have been invited for screening had there been a screening program during the period 1992 through 1997 (age range in 1992, 50-64 years). All women in the control group were invited to undergo a 1-time prevalence screen at the end of their observation period. Screening attendance was similar in both groups (screened, 78.3%, and controls, 79.5%). Counts of incident invasive breast cancers were obtained from the Norwegian Cancer Registry (in situ cancers were excluded)., Results: As expected, before the age-matched controls were invited to be screened at the end of their observation period, the cumulative incidence of invasive breast cancer was significantly higher in the screened group than in the controls (4-year cumulative incidence: 1268 vs 810 per 100 000 population; relative rate, 1.57; 95% confidence interval, 1.44-1.70). Even after prevalence screening in controls, however, the cumulative incidence of invasive breast cancer remained 22% higher in the screened group (6-year cumulative incidence: 1909 vs 1564 per 100 000 population; relative rate, 1.22; 95% confidence interval, 1.16-1.30). Higher incidence was observed in screened women at each year of age., Conclusions: Because the cumulative incidence among controls never reached that of the screened group, it appears that some breast cancers detected by repeated mammographic screening would not persist to be detectable by a single mammogram at the end of 6 years. This raises the possibility that the natural course of some screen-detected invasive breast cancers is to spontaneously regress.

Background: To promote informed decision making about mammography, clinicians are urged to present women with complete, relevant information about breast cancer and screening. Understanding women's current beliefs may help guide such efforts by uncovering misunderstandings, conceptual gaps, and areas of concern., Objective: The authors sought to learn how women view breast cancer, their personal risk of breast cancer, and how screening mammography affects that risk., Methods: Forty-one open-ended semistructured telephone interviews with women selected from a national database by quota sampling to ensure a wide range in demographics of the participants., Results: Almost all respondents viewed breast cancer as a uniformly progressive disease that begins in a silent curable form (typically found by mammograms) and, unless treated early, invariably grows, spreads, and kills. Some women felt that any abnormality found must be treated, even if it was not malignant. None had heard of potentially nonprogressive cancers, and when informed, most felt that the uncertain prognosis of such lesions reinforced the need to find and treat disease as soon as possible. Women expressed a wide range of views about their personal risk of breast cancer. Although some saw breast cancer as a central threat to their health, many others cited heart disease, other cancers, violence, and trauma as greater concerns. Most recognized the importance of "uncontrollable" factors for breast cancer such as age, sex, family history, and genetics. However, other "controllable" factors with little or no demonstrated link to breast cancer (e.g., smoking, diet, toxic exposures, "bad attitudes") were given equal or greater prominence, suggesting that many women feel considerable personal responsibility for their level of breast cancer risk. Similarly, although women recognized that mammography was not perfect, almost all believed that failure to have mammograms put one at risk for premature and preventable death. When asked how mammography worked, almost all repeated the message that "early detection saves lives," suggesting that advanced cancer (and perhaps most cancer deaths) reflected a failure of early detection. The belief in the benefit of early detection was so strong that some women advocated scaring other women into getting mammograms because it is "better to be safe than sorry.", Conclusions: Women view breast cancer as a uniformly progressive disease rarely curable unless caught early. The exaggerated importance many attribute to a variety of controllable factors in modifying personal risk and the "danger" seen in failing to have mammograms may lead women diagnosed with breast cancer to blame themselves.

Objective: To determine women's attitudes and knowledge of both false-positive mammography results and the detection of ductal carcinoma in situ after screening mammography., Design: Cross-sectional survey., Setting: United States., Participants: A total of 479 women aged 18 to 97 years who did not report a history of breast cancer. Main outcome measures Attitudes and knowledge about false-positive results and the detection of ductal carcinoma in situ after screening mammography., Results: Women were aware that false-positive results do occur. Their median estimate of the false-positive rate for 10 years of annual screening was 20% (25th percentile estimate, 10%; 75th percentile estimate, 45%). The women were highly tolerant of false-positive results: 63% thought that 500 or more false-positives per life saved was reasonable, and 37% would tolerate a rate of 10,000 or more. Women who had had a false-positive result (n = 76) expressed the same high tolerance: 30 (39%) would tolerate 10,000 or more false-positives. In all, 62% of women did not want to take false-positive results into account when deciding about screening. Only 8% of women thought that mammography could harm a woman without breast cancer, and 94% doubted the possibility of nonprogressive breast cancers. Few had heard of ductal carcinoma in situ, a cancer that may not progress, but when informed, 60% of women wanted to take into account the possibility of it being detected when deciding about screening., Conclusions: Women are aware of false-positive results and seem to view them as an acceptable consequence of screening mammography. In contrast, most women are unaware that screening can detect cancers that may never progress but think that such information would be relevant. Education should perhaps focus less on false-positive results and more on the less-familiar outcome of the detection of ductal carcinoma in situ.

Objective: To determine women's attitudes to and knowledge of both false positive mammography results and the detection of ductal carcinoma in situ after screening mammography., Design: Cross sectional survey., Setting: United States., Participants: 479 women aged 18-97 years who did not report a history of breast cancer., Main Outcome Measures: Attitudes to and knowledge of false positive results and the detection of ductal carcinoma in situ after screening mammography., Results: Women were aware that false positive results do occur. Their median estimate of the false positive rate for 10 years of annual screening was 20% (25th percentile estimate, 10%; 75th percentile estimate, 45%). The women were highly tolerant of false positives: 63% thought that 500 or more false positives per life saved was reasonable and 37% would tolerate 10 000 or more. Women who had had a false positive result (n=76) expressed the same high tolerance: 39% would tolerate 10 000 or more false positives. 62% of women did not want to take false positive results into account when deciding about screening. Only 8% of women thought that mammography could harm a woman without breast cancer, and 94% doubted the possibility of non-progressive breast cancers. Few had heard about ductal carcinoma in situ, a cancer that may not progress, but when informed, 60% of women wanted to take into account the possibility of it being detected when deciding about screening., Conclusions: Women are aware of false positives and seem to view them as an acceptable consequence of screening mammography. In contrast, most women are unaware that screening can detect cancers that may never progress but feel that such information would be relevant. Education should perhaps focus less on false positives and more on the less familiar outcome of detection of ductal carcinoma in situ.

Background: The fractious public debate over mammography screening recommendations for women aged 40 to 49 years has received extensive attention in medical journals and in the press., Objective: To learn how women interpret the mammography screening debate., Methods: We mailed a survey to a random sample of American women 18 years and older, oversampling women of screening age (40-70 years). Sixty-six percent of women completed the survey (n = 503)., Main Outcome Measures: The main outcome measures were women's reactions to the debate, their suggestion for the starting age for mammography screening, and their understanding of the source of the debate., Results: Almost all women (95%) said that they had paid some attention to the recent discussion about mammography screening. Only 24% said the discussion had improved their understanding of mammography, while 50% reported being upset by the public disagreement among screening experts. Women's beliefs about mammography differed from those articulated by experts in the debate. Eighty-three percent believed that mammography had proven benefit for women aged 40 to 49 years, and 38% believed that benefit was proven for women younger than 40 years. Most women suggested that mammography screening should begin before age 40 years, while only 5% suggested a first mammogram should be performed at 50 years or older. In response to an open-ended question about why mammography has been controversial, 15% cited concerns about the potential harms of radiation and another 12% cited questions about efficacy. Nearly half (49%), however, identified costs as the major source of debate (eg, "Health maintenance organizations [HMOs] don't want to pay for mammography")., Conclusions: Most women paid attention to the recent debate about routine mammography screening for women aged 40 to 49 years, but many believed the debate was about money rather than the question of benefit. Policy makers issuing recommendations about implementation of large-scale mammography screening services need to consider how to effectively disseminate their message.

Background: To provide some sense of the general frequency and timing of diagnostic testing following screening mammography in the United States, we investigated the experience of women screened in the Medicare population., Methods: By use of Medicare's National Claims History System, we identified a cohort (n=23172) of women 65 years old or older screened during the period from January 1, 1995, through April 30, 1995, and tracked each woman over the subsequent 8 months for the performance of additional breast imaging and biopsy procedures. Using two claims-based definitions for newly detected breast cancer, we also estimated the positive predictive value of screening mammography., Results: For every 1000 women aged 65-69 years who underwent screening, 85 (95% confidence interval [CI]=79-91) had follow-up testing in the subsequent 8 months; 76 (95% CI=71-82) had additional breast imaging, and 23 (95% CI=20-26) had biopsy procedures. Corresponding numbers for women aged 70 years or more were similar. Some women underwent repeated examinations; 13% of those receiving diagnostic mammograms had more than one; 11% of those undergoing biopsy procedures had more than one. About half of the women who underwent a biopsy had the procedure more than 3 weeks after the imaging test upon which the decision to perform a biopsy was presumably made. The estimated positive predictive value of an abnormal screening mammogram (defined as a mammogram that engendered additional testing) was 0.08 (95% CI=0.06-0.10) for women aged 65-69 years and 0.14 (95% CI=0.12-0.16) for women aged 70 years or more., Conclusion: Additional testing is a frequent consequence of screening mammography and may require a considerable period of time to come to closure. The need for additional testing, however, is weakly predictive of cancer.

Background: Quantitative information about risks and benefits may be meaningful only to patients who have some facility with basic probability and numerical concepts, a construct called numeracy., Objective: To assess the relation between numeracy and the ability to make use of typical risk reduction expressions about the benefit of screening mammography., Design: Randomized, cross-sectional survey., Setting: A simple random sample of 500 female veterans drawn from a New England registry., Intervention: One of four questionnaires, which differed only in how the same information on average risk reduction with mammography was presented., Measurements: Numeracy was scored as the total number of correct responses to three simple tasks. Participants estimated their risk for death from breast cancer with and without mammography. Accuracy was judged as each woman's ability to adjust her perceived risk in accordance with the risk reduction data presented., Results: 61% of eligible women completed the questionnaire. The median age of these women was 68 years (range, 27 to 88 years), and 96% were high school graduates. Both accuracy in applying risk reduction information and numeracy were poor (one third of respondents thought that 1000 flips of a fair coin would result in < 300 heads). Accuracy was strongly related to numeracy: The accuracy rate was 5.8% (95% CI, 0.8% to 10.7%) for a numeracy score of 0, 8.9% (CI, 2.5% to 15.3%) for a score of 1, 23.7% (CI, 13.9% to 33.5%) for a score of 2, and 40% (CI, 25.1% to 54.9%) for a score of 3., Conclusions: Regardless of how information was presented, numeracy was strongly related to accurately gauging the benefit of mammography. More effective formats are needed to communicate quantitative information about risks and benefits.