Five-year experience with single-view mammography randomized controlled screening in Sweden

The Fundamental Flaws of the CNBSS Trials: A Scientific Review

Although the two Canadian National Breast Screening Study (CNBSS) trials were performed 40 years ago, their negative findings continue to heavily influence screening policies around the world. These policies, based on underestimates of the mortality reduction attributable to mammography particularly for women in the 40-49-year age range, contribute to increased mortality and morbidity from breast cancer. This review summarizes principles of a randomized controlled trial (RCT) and evaluates the compliance of the CNBSS1 and CNBSS2 RCTs in the context of these principles. We describe the fundamental flaws of the CNBSS trials, which failed to demonstrate mortality benefit of screening mammography and contribute to their being the only two outlier studies of eight screening mammography RCTs. The most significant flaws of the trials are (1) inadequate power to detect significant differences in breast cancer mortality; (2) very poor quality mammography with low sensitivity and cancer detection rates; (3) inclusion of women with symptoms of breast cancer; and (4) study design that allowed for violation of the randomization of the allocation process. Finally, we demonstrate that the conditions of the screening intervention in the CNBSS do not reflect the environment of modern population-based screening mammography programs.

Statistical analyses in Swedish randomised trials on mammography screening and in other randomised trials on cancer screening: a systematic review

OBJECTIVES

We compared calculations of relative risks of cancer death in Swedish mammography trials and in other cancer screening trials.

PARTICIPANTS

Men and women from 30 to 74 years of age.

SETTING

Randomised trials on cancer screening.

DESIGN

For each trial, we identified the intervention period, when screening was offered to screening groups and not to control groups, and the post-intervention period, when screening (or absence of screening) was the same in screening and control groups. We then examined which cancer deaths had been used for the computation of relative risk of cancer death.

MAIN OUTCOME MEASURES

Relative risk of cancer death.

RESULTS

In 17 non-breast screening trials, deaths due to cancers diagnosed during the intervention and post-intervention periods were used for relative risk calculations. In the five Swedish trials, relative risk calculations used deaths due to breast cancers found during intervention periods, but deaths due to breast cancer found at first screening of control groups were added to these groups. After reallocation of the added breast cancer deaths to post-intervention periods of control groups, relative risks of 0.86 (0.76; 0.97) were obtained for cancers found during intervention periods and 0.83 (0.71; 0.97) for cancers found during post-intervention periods, indicating constant reduction in the risk of breast cancer death during follow-up, irrespective of screening.

CONCLUSIONS

The use of unconventional statistical methods in Swedish trials has led to overestimation of risk reduction in breast cancer death attributable to mammography screening. The constant risk reduction observed in screening groups was probably due to the trial design that optimised awareness and medical management of women allocated to screening groups.

Quantification of harms in cancer screening trials: literature review

OBJECTIVES

To assess how often harm is quantified in randomised trials of cancer screening.

DESIGN

Two authors independently extracted data on harms from randomised cancer screening trials. Binary outcomes were described as proportions and continuous outcomes with medians and interquartile ranges.

DATA SOURCES

For cancer screening previously assessed in a Cochrane review, we identified trials from their reference lists and updated the search in CENTRAL. For cancer screening not assessed in a Cochrane review, we searched CENTRAL, Medline, and Embase.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Randomised trials that assessed the efficacy of cancer screening for reducing incidence of cancer, cancer specific mortality, and/or all cause mortality.

DATA EXTRACTION

Two reviewers independently assessed articles for eligibility. Two reviewers, who were blinded to the identity of the study's authors, assessed whether absolute numbers or incidence rates of outcomes related to harm were provided separately for the screening and control groups. The outcomes were false positive findings, overdiagnosis, negative psychosocial consequences, somatic complications, invasive follow-up procedures, all cause mortality, and withdrawals because of adverse events.

RESULTS

Out of 4590 articles assessed, 198 (57 trials, 10 screening technologies) matched the inclusion criteria. False positive findings were quantified in two of 57 trials (4%, 95% confidence interval 0% to 12%), overdiagnosis in four (7%, 2% to 18%), negative psychosocial consequences in five (9%, 3% to 20%), somatic complications in 11 (19%, 10% to 32%), use of invasive follow-up procedures in 27 (47%, 34% to 61%), all cause mortality in 34 (60%, 46% to 72%), and withdrawals because of adverse effects in one trial (2%, 0% to 11%). The median percentage of space in the results section that reported harms was 12% (interquartile range 2-19%).

CONCLUSIONS

Cancer screening trials seldom quantify the harms of screening. Of the 57 cancer screening trials examined, the most important harms of screening--overdiagnosis and false positive findings--were quantified in only 7% and 4%, respectively.

Screening for breast cancer with mammography

BACKGROUND

A variety of estimates of the benefits and harms of mammographic screening for breast cancer have been published and national policies vary.

OBJECTIVES

To assess the effect of screening for breast cancer with mammography on mortality and morbidity.

SEARCH METHODS

We searched PubMed (22 November 2012) and the World Health Organization's International Clinical Trials Registry Platform (22 November 2012).

SELECTION CRITERIA

Randomised trials comparing mammographic screening with no mammographic screening.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data. Study authors were contacted for additional information.

MAIN RESULTS

Eight eligible trials were identified. We excluded a trial because the randomisation had failed to produce comparable groups.The eligible trials included 600,000 women in the analyses in the age range 39 to 74 years. Three trials with adequate randomisation did not show a statistically significant reduction in breast cancer mortality at 13 years (relative risk (RR) 0.90, 95% confidence interval (CI) 0.79 to 1.02); four trials with suboptimal randomisation showed a significant reduction in breast cancer mortality with an RR of 0.75 (95% CI 0.67 to 0.83). The RR for all seven trials combined was 0.81 (95% CI 0.74 to 0.87). We found that breast cancer mortality was an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death. The trials with adequate randomisation did not find an effect of screening on total cancer mortality, including breast cancer, after 10 years (RR 1.02, 95% CI 0.95 to 1.10) or on all-cause mortality after 13 years (RR 0.99, 95% CI 0.95 to 1.03).Total numbers of lumpectomies and mastectomies were significantly larger in the screened groups (RR 1.31, 95% CI 1.22 to 1.42), as were number of mastectomies (RR 1.20, 95% CI 1.08 to 1.32). The use of radiotherapy was similarly increased whereas there was no difference in the use of chemotherapy (data available in only two trials).

AUTHORS' CONCLUSIONS

If we assume that screening reduces breast cancer mortality by 15% and that overdiagnosis and overtreatment is at 30%, it means that for every 2000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress including anxiety and uncertainty for years because of false positive findings. To help ensure that the women are fully informed before they decide whether or not to attend screening, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk. Because of substantial advances in treatment and greater breast cancer awareness since the trials were carried out, it is likely that the absolute effect of screening today is smaller than in the trials. Recent observational studies show more overdiagnosis than in the trials and very little or no reduction in the incidence of advanced cancers with screening.

Screening for breast cancer with mammography

BACKGROUND

A variety of estimates of the benefits and harms of mammographic screening for breast cancer have been published and national policies vary.

OBJECTIVES

To assess the effect of screening for breast cancer with mammography on mortality and morbidity.

SEARCH STRATEGY

We searched PubMed (November 2008).

SELECTION CRITERIA

Randomised trials comparing mammographic screening with no mammographic screening.

DATA COLLECTION AND ANALYSIS

Both authors independently extracted data. Study authors were contacted for additional information.

MAIN RESULTS

Eight eligible trials were identified. We excluded a biased trial and included 600,000 women in the analyses. Three trials with adequate randomisation did not show a significant reduction in breast cancer mortality at 13 years (relative risk (RR) 0.90, 95% confidence interval (CI) 0.79 to 1.02); four trials with suboptimal randomisation showed a significant reduction in breast cancer mortality with an RR of 0.75 (95% CI 0.67 to 0.83). The RR for all seven trials combined was 0.81 (95% CI 0.74 to 0.87). We found that breast cancer mortality was an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death. The trials with adequate randomisation did not find an effect of screening on cancer mortality, including breast cancer, after 10 years (RR 1.02, 95% CI 0.95 to 1.10) or on all-cause mortality after 13 years (RR 0.99, 95% CI 0.95 to 1.03).Numbers of lumpectomies and mastectomies were significantly larger in the screened groups (RR 1.31, 95% CI 1.22 to 1.42) for the two adequately randomised trials that measured this outcome; the use of radiotherapy was similarly increased.

AUTHORS' CONCLUSIONS

Screening is likely to reduce breast cancer mortality. As the effect was lowest in the adequately randomised trials, a reasonable estimate is a 15% reduction corresponding to an absolute risk reduction of 0.05%. Screening led to 30% overdiagnosis and overtreatment, or an absolute risk increase of 0.5%. This means that for every 2000 women invited for screening throughout 10 years, one will have her life prolonged and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress for many months because of false positive findings. It is thus not clear whether screening does more good than harm. To help ensure that the women are fully informed of both benefits and harms before they decide whether or not to attend screening, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk.

Screening for breast cancer with mammography

BACKGROUND

A variety of estimates of the benefits and harms of mammographic screening for breast cancer have been published and national policies vary.

OBJECTIVES

To assess the effect of screening for breast cancer with mammography on mortality and morbidity.

SEARCH STRATEGY

We searched PubMed (November 2008).

SELECTION CRITERIA

Randomised trials comparing mammographic screening with no mammographic screening.

DATA COLLECTION AND ANALYSIS

Both authors independently extracted data. Study authors were contacted for additional information.

MAIN RESULTS

Eight eligible trials were identified. We excluded a biased trial and included 600,000 women in the analyses. Three trials with adequate randomisation did not show a significant reduction in breast cancer mortality at 13 years (relative risk (RR) 0.90, 95% confidence interval (CI) 0.79 to 1.02); four trials with suboptimal randomisation showed a significant reduction in breast cancer mortality with an RR of 0.75 (95% CI 0.67 to 0.83). The RR for all seven trials combined was 0.81 (95% CI 0.74 to 0.87). We found that breast cancer mortality was an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death. The trials with adequate randomisation did not find an effect of screening on cancer mortality, including breast cancer, after 10 years (RR 1.02, 95% CI 0.95 to 1.10) or on all-cause mortality after 13 years (RR 0.99, 95% CI 0.95 to 1.03).Numbers of lumpectomies and mastectomies were significantly larger in the screened groups (RR 1.31, 95% CI 1.22 to 1.42) for the two adequately randomised trials that measured this outcome; the use of radiotherapy was similarly increased.

AUTHORS' CONCLUSIONS

Screening is likely to reduce breast cancer mortality. As the effect was lowest in the adequately randomised trials, a reasonable estimate is a 15% reduction corresponding to an absolute risk reduction of 0.05%. Screening led to 30% overdiagnosis and overtreatment, or an absolute risk increase of 0.5%. This means that for every 2000 women invited for screening throughout 10 years, one will have her life prolonged and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress for many months because of false positive findings. It is thus not clear whether screening does more good than harm. To help ensure that the women are fully informed of both benefits and harms before they decide whether or not to attend screening, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk.

[Mammography screening in Germany]

Available data suggest that early detection of breast cancer by mammography screening can reduce mortality by about 25%. Intensified monitoring of women with a family history of breast cancer and regular general screening have recently been introduced in Germany. The screening program is expected to be fully established by 2008. Following its successful introduction (participation rates between 65 and 80%), the German screening program will be conducted and evaluated in accordance with the European guidelines. At least in the screening trials that were conducted prior to the now established screening program the quality criteria were more than fulfilled (e.g. cancer detection rate in Bremen 8.7, Wiesbaden 9.4, Weser-Ems region 8.3/1000). Additional parameters that can be taken into account for quality assurance are the overdiagnosis bias, lead time bias, length bias and selection bias. Moreover, there are some factors that are specific to the German program compared with the breast cancer screening programs already established in other countries. One of these is the intensified screening program for high-risk women (ca. 5% of all carcinomas) and as a result fewer women with an increased genetic risk of breast cancer will be represented in the general screening program. The German screening program involves only a few university centers and hospital-based physicians, which may have adverse effects on research and development as well as mammography training in the future. Therefore, the screening program should also provide for the investigation of new techniques or emerging techniques (e.g. CAD systems in screening mammography) in the future.

Screening for breast cancer with mammography

BACKGROUND

A variety of estimates of the benefits and harms of mammographic screening for breast cancer have been published and national policies vary.

OBJECTIVES

To assess the effect of screening for breast cancer with mammography on mortality and morbidity.

SEARCH STRATEGY

We searched PubMed (June 2005).

SELECTION CRITERIA

Randomised trials comparing mammographic screening with no mammographic screening.

DATA COLLECTION AND ANALYSIS

Both authors independently extracted data. Study authors were contacted for additional information.

MAIN RESULTS

Seven completed and eligible trials involving half a million women were identified. We excluded a biased trial from analysis. Two trials with adequate randomisation did not show a significant reduction in breast cancer mortality, relative risk (RR) 0.93 (95% confidence interval 0.80 to 1.09) at 13 years; four trials with suboptimal randomisation showed a significant reduction in breast cancer mortality, RR 0.75 (0.67 to 0.83) (P = 0.02 for difference between the two estimates). RR for all six trials combined was 0.80 (0.73 to 0.88). The two trials with adequate randomisation did not find an effect of screening on cancer mortality, including breast cancer, RR 1.02 (0.95 to 1.10) after 10 years, or on all-cause mortality, RR 1.00 (0.96 to 1.04) after 13 years. We found that breast cancer mortality was an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death. Numbers of lumpectomies and mastectomies were significantly larger in the screened groups, RR 1.31 (1.22 to 1.42) for the two adequately randomised trials; the use of radiotherapy was similarly increased.

AUTHORS' CONCLUSIONS

Screening likely reduces breast cancer mortality. Based on all trials, the reduction is 20%, but as the effect is lower in the highest quality trials, a more reasonable estimate is a 15% relative risk reduction. Based on the risk level of women in these trials, the absolute risk reduction was 0.05%. Screening also leads to overdiagnosis and overtreatment, with an estimated 30% increase, or an absolute risk increase of 0.5%. This means that for every 2000 women invited for screening throughout 10 years, one will have her life prolonged. In addition, 10 healthy women, who would not have been diagnosed if there had not been screening, will be diagnosed as breast cancer patients and will be treated unnecessarily. It is thus not clear whether screening does more good than harm. Women invited to screening should be fully informed of both benefits and harms.

Increased incidence of invasive breast cancer after the introduction of service screening with mammography in Sweden

Screening with mammography has been shown to substantially reduce mortality from breast cancer. The incidence of invasive cancer will increase as screening starts, and it is desirable that it gradually returns to the same level as before screening. Age-specific incidence of invasive breast cancer in 11 Swedish counties, including 463,000 women aged 40-74 years, was analysed before and after the start of service screening with mammography. Incidence, as observed on average during 12.8 years from screening start, was compared to expected incidence based on the incidence during a 15-year period preceding screening start. The height of the incidence peak during the first screening round was increasing with increasing age, compatible with the accumulation in the population of slowly growing tumours by age. All analysed age groups showed an increased ratio between observed stabilised incidence 7-14 years after screening start and expected incidence. When relative risks were adjusted for lead time, the estimates were 1.54 (95% confidence interval [CI] 1.33-1.79) and 1.21 (95% CI 1.04-1.41) for the age groups 50-59 and 60-69 years, respectively. In the age groups 40-49 and 70-74, no change was observed. The findings were further confirmed by the observation of a disappearance in the screened population of the notch in the increasing trend of age-specific breast cancer incidence for the ages after menopause. This notch could indicate hormone-related retardation in tumour growth around menopause. It appears that many of these clinically insignificant, retarded tumours are detected with screening mammography.

Screening sensitivity and sojourn time from breast cancer early detection clinical trials: mammograms and physical examinations

PURPOSE

To estimate sensitivities of breast cancer screening modalities and preclinical duration of the disease from eight breast cancer screening clinical trials.

PATIENTS AND METHODS

Screening programs invariably lead to diagnosis of disease before signs or symptoms are present. Two key quantities of screening programs are the sensitivity of the disease detection modality and the mean sojourn time (MST). The observed screening histories in a periodically screened cohort make it possible to estimate these quantities of interest. We applied recently developed statistical methods to data from eight randomized breast cancer screening trials to estimate the sensitivities of early detection modalities and MST. Moreover, when a screening trial involved two screening modalities, our methods enabled the estimation of the individual sensitivity of each screening modality.

RESULTS

We analyzed breast cancer data from several screening trials and have relatively complete data from the Health Insurance Plan (HIP), Edinburgh, and two Canadian studies. The screening sensitivity for mammography, physical examination, and MST were, respectively, HIP: 0.39, 0.47, and 2.5 years; Edinburgh: 0.63, 0.40, and 4.3 years; Canadian (age 40 to 49 at entry): 0.61, 0.59, and 1.9 years; Canadian (age 50 to 59 at entry): 0.66, 0.39, and 3.1 years.

CONCLUSION

The public debate on early breast cancer detection is mainly centered on mammograms. However, the current study indicates that a physical examination is of comparable importance. Cautious interpretation of trial differences is required as a result of various experimental designs and the age dependency of screening sensitivity and MST.

Sensitivity, specificity and predictive values of breast imaging in the detection of cancer

In an observational follow-up study we determined whether the combined use of mammography and breast ultrasonography is an appropriate diagnostic tool to select patients with symptomatic breast disease who need additional pathological evaluation. Mammography and ultrasound were used as complementary diagnostic modalities in 3014 consecutively referred and mainly symptomatic patients. Sensitivity, specificity, predictive values and likelihood ratios were calculated according to standard procedures. Virtually complete follow-up was obtained by correlating the radiological diagnosis with clinical records, final pathological findings, records from the Cancer Register and data from questionnaires sent to the general practitioners of all the referred patients. After an average follow-up period of 30 months, the sensitivity for breast cancer detection was 92.0% and the specificity 97.7%. A positive predictive value of 68.0%, a negative predictive value of 99.6%, a positive likelihood ratio of 40 and a negative likelihood ratio of 0.08 were found. The mean diagnostic delay as a result of false negative examinations was 9 months (range 0-20 months). We conclude that breast imaging in routine daily practice, consisting of the integral use of mammography and ultrasonography, is an appropriate tool in the detection of cancer and should be included in the work-up of symptomatic breast disease.

The South Australian Breast X-Ray Service: results from a statewide mammographic screening programme

The South Australian Breast X-Ray Service is a centralised breast cancer screening programme in the State of South Australia. In its first 5 years of operation nearly 100 000 screens were performed. This study reports the clinical performance of the programme and compares it with other published series. Women aged 40 years and over were screened with two-view mammography every 2 years. Radiologists double-read the screening films and multidisciplinary teams assessed the recalled women at a single centre. In the prevalent round 76 106 women were screened, and subsequently 21 506 of them were rescreened. The recall rate for further investigation was 4.9% in the prevalent round and 2.4% in the incident rounds. The cancer detection rate per 1000 women was 7.0 in the prevalent screening round and 3.4 in the incident rounds. Forty-two per cent of invasive carcinomas measured < or = 10 mm in the prevalent screening round and the median tumour size was 12 mm. The benign to malignant biopsy ratio was 1:1.4 in the prevalent round and 1:2.8 in the incident rounds. In the prevalent round 77% of invasive tumours were lymph node negative and this proportion increased to 86% in the incident rounds.

Mammography screening guidelines for women 40 to 49 and over 65 years old

Many organizations in the United States recommend mammography screening at 1- to 2-year intervals for those 40 to 49 years old. In most areas of Canada and Europe, screening mammography is not recommended for women 40 to 49 years old. These differences have arisen over interpretation of data from the Health Insurance Plan (HIP) study and the Breast Cancer Detection Demonstration Project (BCDDP). The apparent benefit in the HIP study is probably attributable to poor survival of control subjects with stage 1 cancers. In the BCDDP, although high cancer detection rates by mammography and improved survival of patients with screen-detected cancer were seen, the latter was probably largely due to lead time bias. The screening studies in Canada and Europe show no evidence of effectiveness of mammography screening in women 40 to 49 years old, at least in the first 10 years after screening is initiated. For women over 65 there are few data, but screening to age 74 is probably appropriate.

The Stockholm breast cancer screening trial--5-year results and stage at discovery

In screening programmes it is important to assess a preliminary effectiveness of the screening method as soon as possible in order to forecast survival figures. In March 1981 a controlled single-view mammographic screening trial for breast cancer was started in the south of Stockholm. The population invited for screening mammography consisted of 40,000 women aged 40-64 years, and 20,000 women served as a well-defined control group. The main aim of the trial was to determine whether repeated mammographic screening could reduce the mortality in the study population (SP) compared to the control population (CP). The cumulative number of advanced mammary carcinomas in the screening and the control populations from the first five years of screening have shown a tendency towards more favourable stages in the screened population aged 40-64 years. A breakdown by age suggests an effect in age group 50-59 years, but not yet in age groups 40-49 and 60-64 years. When comparing the rates of stage II+ cancer, an increased number is found in the study group. As the total rate of breast cancer is higher in SP than in CP, there ought to be a concealed group of stage II+ cancers in the CP which makes the comparison biased. A new approach has been designed, where an estimation of the 'hidden' number of stage II+ cancers in CP is added to the clinically detected cases, and in this respect a comparison has shown a decrease in the cumulative number of advanced cancers in the SP in relation to the CP (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Mass screening for breast cancer

Breast cancer is now the most common cancer in women. There is a certain correlation between the stage of the disease at diagnosis and outcome after treatment. Several studies have been initiated involving mammography with or without physical examination aimed at early detection of breast cancer in asymptomatic women. In order to review the results to date, a meeting was held in Reykjavík in April 1984 organized by international and Icelandic health agencies and attended by senior investigators of the ongoing screening studies. A summary of the available data is presented in this paper along with the conclusions of the meeting.

Randomized mammographic screening for breast cancer in Stockholm. Design, first round results and comparisons

In March 1981 a randomized single-view mammographic screening for breast cancer was started in the south of Stockholm. The screened population in the first round numbered 40,318 women, and 20,000 women served as a well-defined control group. The age groups represented were 40-64 years, and 80.7% of the invited women participated in the study. The first round disclosed 128 breast cancers (113 invasive and 15 noninvasive), or 4.0 per 1,000 women. Mean tumour size was 14.1 mm and axillary lymph node metastases were found in 21.8%. Fifty-five per cent of the tumours were small (less than or equal to 10 mm) or non-invasive, and 71% were stage I. Participation rates are high in all Swedish trials. The present results differ only slightly from other screening programs; the percentages of patients with axillary metastases and stage II tumours are similar in the Stockholm, Malmö and Kopparberg/Ostergötland studies. Comparisons of cancer prevalence in the various Swedish screening trials show that, in comparable age groups, there are some differences, even when the differences in the natural cancer incidence are taken into account. A decreased mortality was found recently in a Swedish trial in ages above 50 years but not below. In the Stockholm study more than one-third of the participants were aged 40-49 years.