Understanding recent trends in incidence of invasive breast cancer in Norway: age-period-cohort analysis based on registry data on mammography screening and hormone treatment use

Non-progressive breast carcinomas detected at mammography screening: a population study

BACKGROUND

Some breast carcinomas detected at screening, especially ductal carcinoma in situ, may have limited potential for progression to symptomatic disease. To determine non-progression is a challenge, but if all screening-detected breast tumors eventually reach a clinical stage, the cumulative incidence at a reasonably high age would be similar for women with or without screening, conditional on the women being alive.

METHODS

Using high-quality population data with 24 years of follow-up from the gradually introduced BreastScreen Norway program, we studied whether all breast carcinomas detected at mammography screening 50-69 years of age would progress to clinical symptoms within 85 years of age. First, we estimated the incidence rates of breast carcinomas by age in scenarios with or without screening, based on an extended age-period-cohort incidence model. Next, we estimated the frequency of non-progressive tumors among screening-detected cases, by calculating the difference in the cumulative rate of breast carcinomas between the screening and non-screening scenarios at 85 years of age.

RESULTS

Among women who attended BreastScreen Norway from the age of 50 to 69 years, we estimated that 1.1% of the participants were diagnosed with a breast carcinoma without the potential to progress to symptomatic disease by 85 years of age. This proportion of potentially non-progressive tumors corresponded to 15.7% [95% CI 3.3, 27.1] of breast carcinomas detected at screening.

CONCLUSIONS

Our findings suggest that nearly one in six breast carcinomas detected at screening may be non-progressive.

Temporal Pattern and Age-Period-Cohort Analysis of Breast Cancer Incidence in Iranian Women (2009-2017)

BACKGROUND

Breast cancer accounted for 28.1% of all female cancers in 2020 in Iran. This study was conducted to evaluate the time trend of breast cancer incidence and to identify the changes of breast cancer incidence in age, period, and birth cohorts in Iran, in the 2009-2017 timeframe.

METHODS

Annual cancer statistics for female breast cancer were obtained from the Iranian National Population-based Cancer Registry (INPCR) database from 2009 to 2017. The age-period-cohort (APC) analysis was used to evaluate the time trend of breast cancer incidence in age, period and birth cohorts between 2009 and 2017. R package (Epi) was used to analyze data. Results were considered statistically significant at P<0.05.

RESULTS

The age effect showed an increased incidence of breast cancer until the age of 45, and after this age the speed of increase was slower until 65 years. There was an increased diagnosis in 2015-2017 (period effect) for many age groups, especially in the 70- and over 80-year-old group.

CONCLUSION

Our findings indicated that breast cancer incidence peaks in the age of 45 in Iranian women, which is a decade earlier compared to the Western world. The period effect in 2015-2017 can be explained by the fact that in 2014, the former Iranian pathology-based cancer registry was upgraded to a population-based cancer registry, which resulted in improved coverage of cancer registry and case finding.

Long term trends of breast cancer incidence according to proliferation status

BACKGROUND

Long-term breast cancer incidence trends according to proliferation status are poorly described. We studied time-trends in breast cancer incidence, using mitotic count and Ki-67 as markers of proliferation.

METHODS

Among 83,298 Norwegian women followed for breast cancer occurrence 1961-2012, 2995 incident breast cancers were diagnosed. Ki-67 was assessed using immunohistochemistry on tissue microarrays and mitoses were counted on whole sections. We compared incidence rates according to proliferation status among women born 1886-1928 and 1929-1977, estimating age-specific incidence rate ratios. We performed multiple imputations to account for unknown proliferation status. Mean values of Ki-67 and mitotic counts were calculated, according to age and birth year. We performed separate incidence analyses for HER2⁺ and triple negative breast cancers.

RESULTS

Among women aged 40-69 years, incidence rates of tumours with low-proliferative activity were higher among those born in 1929 or later, compared to before 1929, according to Ki-67 and mitotic count. Incidence rates of tumours with high-proliferative activity were also higher in women born in 1929 or later compared to before 1929 according to Ki-67, but not according to mitotic count. Mean values of Ki-67 and mitotic count varied according to age and birth year. In subtype-specific analyses we found an increase of high-proliferative HER2⁺ tumours according to Ki-67 in women born in 1929 or later, compared to before 1929.

CONCLUSIONS

There has been a temporal increase in both low- and high-proliferative breast cancers.

Breast cancer screening and overdiagnosis

Overdiagnosis is a harmful consequence of screening which is particularly challenging to estimate. An unbiased setting to measure overdiagnosis in breast cancer screening requires comparative data from a screened and an unscreened cohort for at least 30 years. Such randomised data will not become available, leaving us with observational data over shorter time periods and outcomes of modelling. This collaborative effort of the International Cancer Screening Network quantified the variation in estimated breast cancer overdiagnosis in organised programmes with evaluation of both observed and simulated data, and presented examples of how modelling can provide additional insights. Reliable observational data, analysed with study design accounting for methodological pitfalls, and modelling studies with different approaches, indicate that overdiagnosis accounts for less than 10% of invasive breast cancer cases in a screening target population of women aged 50 to 69. Estimates above this level are likely to derive from inaccuracies in study design. The widely discrepant estimates of overdiagnosis reported from observational data could substantially be reduced by use of a cohort study design with at least 10 years of follow-up after screening stops. In contexts where concomitant opportunistic screening or gradual implementation of screening occurs, and data on valid comparison groups are not readily available, modelling of screening intervention becomes an advantageous option to obtain reliable estimates of breast cancer overdiagnosis.

Estimating the natural progression of non-invasive ductal carcinoma in situ breast cancer lesions using screening data

OBJECTIVES

In addition to invasive breast cancer, mammography screening often detects preinvasive ductal carcinoma in situ (DCIS) lesions. The natural progression of DCIS is largely unknown, leading to uncertainty regarding treatment. The natural history of invasive breast cancer has been studied using screening data. DCIS modeling is more complicated because lesions might progress to clinical DCIS, preclinical invasive cancer, or may also regress to a state undetectable by screening. We have here developed a Markov model for DCIS progression, building on the established invasive breast cancer model.

METHODS

We present formulas for the probability of DCIS detection by time since last screening under a Markov model of DCIS progression. Progression rates were estimated by maximum likelihood estimation using BreastScreen Norway data from 1995-2002 for 336,533 women (including 399 DCIS cases) aged 50-69. As DCIS incidence varies by age, county, and mammography modality (digital vs. analog film), a Poisson regression approach was used to align the input data.

RESULTS

Estimated mean sojourn time in preclinical, screening-detectable DCIS phase was 3.1 years (95% confidence interval: 1.3, 7.6) with a screening sensitivity of 60% (95% confidence interval: 32%, 93%). No DCIS was estimated to be non-progressive.

CONCLUSION

Most preclinical DCIS lesions progress or regress with a moderate sojourn time in the screening-detectable phase. While DCIS mean sojourn time could be deduced from DCIS data, any estimate of preclinical DCIS progressing to invasive breast cancer must include data on invasive cancers to avoid strong, probably unrealistic, assumptions.

Age-period-cohort analysis with a constant-relative-variation constraint for an apportionment of period and cohort slopes

Age-period-cohort analysis of incidence and/or mortality data has received much attention in the literature. To circumvent the non-identifiability problem inherent in the age-period-cohort model, additional constraints are necessary on the parameters estimates. We propose setting the constraint to reflect the different nature of the three temporal variables: age, period, and birth cohort. There are two assumptions in our method. Recognizing age effects to be deterministic (first assumption), we do not explicitly incorporate the age parameters into constraint. For the stochastic period and cohort effects, we set a constant-relative-variation constraint on their trends (second assumption). The constant-relative-variation constraint dictates that between two stochastic effects, one with a larger curvature gets a larger (absolute) slope, and one with zero curvature gets no slope. We conducted Monte-Carlo simulations to examine the statistical properties of the proposed method and analyzed the data of prostate cancer incidence for whites from 1973-2012 to illustrate the methodology. A driver for the period and/or cohort effect may be lacking in some populations. In that case, the CRV method automatically produces an unbiased age effect and no period and/or cohort effect, thereby addressing the situation properly. However, the method proposed in this paper is not a general purpose model and will produce biased results in many other real-life data scenarios. It is only useful in situations when the age effects are deterministic and dominant, and the period and cohort effects are stochastic and minor.

Simulating the Impact of Risk-Based Screening and Treatment on Breast Cancer Outcomes with MISCAN-Fadia

The MISCAN-Fadia microsimulation model uses continuous tumor growth to simulate the natural history of breast cancer and has been used extensively to estimate the impact of screening and adjuvant treatment on breast cancer incidence and mortality trends. The model simulates individual life histories from birth to death, with and without breast cancer, in the presence and in the absence of screening and treatment. Life histories are simulated according to discrete events such as birth, tumor inception, the tumor's clinical diagnosis diameter in the absence of screening, and death from breast cancer or death from other causes. MISCAN-Fadia consists of 4 main components: demography, natural history of breast cancer, screening, and treatment. Screening impact on the natural history of breast cancer is assessed by simulating continuous tumor growth and the "fatal diameter" concept. This concept implies that tumors diagnosed at a size that is between the screen detection threshold and the fatal diameter are cured, while tumors diagnosed at a diameter larger than the fatal tumor diameter metastasize and lead to breast cancer death. MISCAN-Fadia has been extended by including a different natural history for molecular subtypes based on a tumor's estrogen receptor (ER) status and human epidermal growth factor receptor 2 (HER2) status. In addition, personalized screening strategies that target women based on their risk such as breast density have been incorporated into the model. This personalized approach to screening will continue to develop in light of potential polygenic risk stratification possibilities and new screening modalities.

As you like it: How the same data can support manifold views of overdiagnosis in breast cancer screening

Overdiagnosis estimates have varied substantially, causing confusion. The discussions have been complicated by the fact that population and study design have varied substantially between studies. To help assess the impact of study design choices on the estimates, we compared them on a single population. A cohort study from Funen County, Denmark, recently suggested little (∼1%) overdiagnosis. It followed previously screened women for up to 14 years after screening had ended. Using publically available data from Funen, we recreated the designs from five high-estimate, highly cited studies from various countries. Selected studies estimated overdiagnosis to be 25-54%. Their designs were adapted only to the extent that they reflect the start of screening in Funen in 1993. The reanalysis of the Funen data resulted in overdiagnosis estimates that were remarkably similar to those from the original high-estimate age-period studies, 21-55%. In additional analyses, undertaken to elucidate the effect of the individual components of the study designs, overdiagnosis estimates were more than halved after the most likely changes in the background risk were accounted for and decreased additionally when never-screened birth cohorts were excluded from the analysis. The same data give both low and high estimates of overdiagnosis, it all depends on the study design. This stresses the need for a careful scrutiny of the validity of the assumptions underpinning the estimates. Age-period analyses of breast cancer overdiagnosis suggesting very high frequencies of overdiagnosis rested on unmet assumptions. This study showed that overdiagnosis estimates should in the future be requested to adequately control for the background risk and include an informative selection of the studied population to achieve valid and comparable estimates of overdiagnosis.

Common Model Inputs Used in CISNET Collaborative Breast Cancer Modeling

BACKGROUND

Since their inception in 2000, the Cancer Intervention and Surveillance Network (CISNET) breast cancer models have collaborated to use a nationally representative core of common input parameters to represent key components of breast cancer control in each model. Employment of common inputs permits greater ability to compare model output than when each model begins with different input parameters. The use of common inputs also enhances inferences about the results, and provides a range of reasonable results based on variations in model structure, assumptions, and methods of use of the input values. The common input data are updated for each analysis to ensure that they reflect the most current practice and knowledge about breast cancer. The common core of parameters includes population rates of births and deaths; age- and cohort-specific temporal rates of breast cancer incidence in the absence of screening and treatment; effects of risk factors on incidence trends; dissemination of plain film and digital mammography; screening test performance characteristics; stage or size distribution of screen-, interval-, and clinically- detected tumors by age; the joint distribution of ER/HER2 by age and stage; survival in the absence of screening and treatment by stage and molecular subtype; age-, stage-, and molecular subtype-specific therapy; dissemination and effectiveness of therapies over time; and competing non-breast cancer mortality.

METHOD AND RESULTS

In this paper, we summarize the methods and results for the common input values presently used in the CISNET breast cancer models, note assumptions made because of unobservable phenomena and/or unavailable data, and highlight plans for the development of future parameters.

CONCLUSION

These data are intended to enhance the transparency of the breast CISNET models.

Changing patterns of breast cancer incidence and mortality by education level over four decades in Norway, 1971-2009

Background

In the last century, breast cancer incidence and mortality was higher among higher versus lower educated women in developed countries. Post-millennium, incidence rates have flattened off and mortality declined. We examined breast cancer trends by education level, to see whether recent improvements in incidence and mortality rates have occurred in all education groups.

Methods

We linked individual registry data on female Norwegian inhabitants aged 35 years and over during 1971–2009. Using Poisson models, we calculated absolute and relative educational differences in age-standardised breast cancer incidence and mortality over four decades. We estimated educational differences by Slope and Relative Index of Inequality, which correspond to rate difference and rate ratio, comparing the highest to lowest educated women.

Results

Pre-millennium, incidence and mortality of breast cancer were significantly higher in higher versus lower educated women. Post-millennium, educational differences in breast cancer incidence and mortality attenuated. During 2000–2009, breast cancer incidence was still 38% higher for higher versus lower educated women (Relative Index of Inequality: 1.38, 95% confidence interval: 1.31–1.44), but mortality no longer varied significantly by education level (Relative Index of Inequality: 1.09, 95% confidence interval: 0.99–1.19). Among women below 50 years, however, the education gradient for mortality reversed, and mortality was 28% lower for the highest versus lowest educated women during 2000–2009 (Relative Index of Inequality: 0.72, 95% confidence interval: 0.51–0.93).

Results

Post-millennium improvements in breast cancer incidence and mortality have primarily benefited higher educated women. Breast cancer mortality is now highest among the lowest educated women below 50 years.

Evaluating different breast tumor progression models using screening data

Background

Mammography screening is used to detect breast cancer at an early treatable stage, reducing breast cancer mortality. Traditionally, breast cancer has been seen as a disease with only progressive lesions, and here we examine the validity of this assumption by testing if incidence levels after introducing mammography screening can be reproduced assuming only progressive tumors.

Methods

Breast cancer incidence data 1990–2009 obtained from the initially screened Norwegian counties (Akershus, Oslo, Rogaland and Hordaland) was included, covering the time-period before, during and after the introduction of mammography screening. From 1996 women aged 50–69 were invited for biennial public screening. Using estimates of tumor growth and screening sensitivity based on pre-screening and prevalence screening data (1990–1998), we simulated incidence levels during the following period (1999–2009).

Results

The simulated incidence levels during the period with repeated screenings were markedly below the observed levels. The results were robust to changes in model parameters. Adjusting for hormone replacement therapy use, we obtained levels closer to the observed levels. However, there was still a marked gap, and only by assuming some tumors that undergo regressive changes or enter a markedly less detectable state, was our model able to reproduce the observed incidence levels.

Conclusions

Models with strictly progressive tumors are only able to partly explain the changes in incidence levels observed after screening introduction in the initially screened Norwegian counties. More complex explanations than a time shift in detection of future clinical cancers seem to be needed to reproduce the incidence trends, questioning the basis for many over-diagnosis calculations. As data are not randomized, similar studies in other populations are wanted to exclude effect of unknown confounders.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4130-2) contains supplementary material, which is available to authorized users.

Cost-effectiveness of the Norwegian breast cancer screening program

The Norwegian Breast Cancer Screening Programme (NBCSP) has a nation-wide coverage since 2005. All women aged 50-69 years are invited biennially for mammography screening. We evaluated breast cancer mortality reduction and performed a cost-effectiveness analysis, using our microsimulation model, calibrated to most recent data. The microsimulation model allows for the comparison of mortality and costs between a (hypothetical) situation without screening and a situation with screening. Breast cancer incidence in Norway had a steep increase in the early 1990s. We calibrated the model to simulate this increase and included recent costs for screening, diagnosis and treatment of breast cancer and travel and productivity loss. We estimate a 16% breast cancer mortality reduction for a cohort of women, invited to screening, followed over their complete lifetime. Cost-effectiveness is estimated at NOK 112,162 per QALY gained, when taking only direct medical costs into account (the cost of the buses, examinations, and invitations). We used a 3.5% annual discount rate. Cost-effectiveness estimates are substantially below the threshold of NOK 1,926,366 as recommended by the WHO guidelines. For the Norwegian population, which has been gradually exposed to screening, breast cancer mortality reduction for women exposed to screening is increasing and is estimated to rise to ∼30% in 2020 for women aged 55-80 years. The NBCSP is a highly cost-effective measure to reduce breast cancer specific mortality. We estimate a breast cancer specific mortality reduction of 16-30%, at the cost of 112,162 NOK per QALY gained.

Breast cancer incidence trends in Norway and estimates of overdiagnosis

Objective

Fluctuations in the incidence of breast cancer in Norway in the last three decades are partly explained by the use of hormone replacement therapy and mammography screening, but overdiagnosis has also been suggested as a cause. We assessed the trends in breast cancer incidence and overdiagnosis in Norway.

Methods

We calibrated our microsimulation model to Norwegian Cancer Registration data. The model takes into account the use of mammography (both within and outside the Norwegian Breast Cancer Screening Programme) and of hormone replacement therapy. We obtained a proper fit of breast cancer incidence in recent years, when assuming an increase in the background risk for breast cancer, and estimated overdiagnosis.

Results

We estimated a 2% overdiagnosis rate as a fraction of all cancers diagnosed in women aged 50–100, and a 3% overdiagnosis rate as a fraction of all cancers diagnosed in women aged 50–70 (i.e. screening age). If all of the increased incidence would be the result of the detection of slow growing tumours, these estimates were 7% and 11%, respectively.

Conclusion

Besides mammography and hormone replacement therapy use, additional risk factors contributed to the sudden increase in breast cancer incidence in Norway. Overdiagnosis estimates due to screening were within the range of international plausible estimates.

Breast cancer risk and protracted low-to-moderate dose occupational radiation exposure in the US Radiologic Technologists Cohort, 1983-2008

Background:

Although high-dose ionising radiation is associated with increased breast cancer risks, the association with protracted low-dose-rate exposures remains unclear. The US Radiologic Technologist study provides an opportunity to examine the association between low-to-moderate dose radiation and breast cancer incidence and mortality.

Methods:

One thousand nine hundred and twenty-two self-reported first primary cancers were diagnosed during 1983–2005 among 66 915 female technologists, and 586 breast cancer deaths occurred during 1983–2008 among 83 538 female cohort members. Occupational breast dose estimates were based on work histories, historical data, and, after the mid-1970s, individual film badge measurements. Excess relative risks were estimated using Poisson regression with birth cohort stratification and adjustment for menopause, reproductive history, and other risk factors.

Results:

Higher doses were associated with increased breast cancer incidence, with an excess relative risk at 100 mGy of 0.07 (95% confidence interval (CI): -0.005 to 0.19). Associations were strongest for technologists born before 1930 (excess relative risk at 100 mGy=0.16; 95% CI: 0.03–0.39) with similar patterns for mortality among technologists born before 1930.

Conclusions:

Occupational radiation to the breast was positively associated with breast cancer risk. The risk was more pronounced for women born before 1930 who began working before 1950 when mean annual doses (37 mGy) were considerably higher than in later years (1.3 mGy). However, because of the uncertainties and possible systematic errors in the occupational dose estimates before 1960, these findings should be treated with caution.

Balancing the benefits and detriments among women targeted by the Norwegian Breast Cancer Screening Program

Objective

To compute a ratio between the estimated numbers of lives saved from breast cancer death and the number of women diagnosed with a breast cancer that never would have been diagnosed during the woman’s lifetime had she not attended screening (epidemiologic over-diagnosis) in the Norwegian Breast Cancer Screening Program.

Methods

The Norwegian Breast Cancer Screening Program invites women aged 50–69 to biennial mammographic screening. Results from published studies using individual level data from the programme for estimating breast cancer mortality and epidemiologic over-diagnosis comprised the basis for the ratio. The mortality reduction varied from 36.8% to 43% among screened women, while estimates on epidemiologic over-diagnosis ranged from 7% to 19.6%. We computed the average estimates for both values. The benefit–detriment ratio, number of lives saved, and number of women over-diagnosed were computed for different scenarios of reduction in breast cancer mortality and epidemiologic over-diagnosis.

Results

For every 10,000 biennially screened women, followed until age 79, we estimated that 53–61 (average 57) women were saved from breast cancer death, and 45–126 (average 82) were over-diagnosed. The benefit–detriment ratio using average estimates was 1:1.4, indicating that the programme saved about one life per 1–2 women with epidemiologic over-diagnosis.

Conclusion

The benefit–detriment ratio estimates of the Norwegian Breast Cancer Screening Program, expressed as lives saved from breast cancer death and epidemiologic over-diagnosis, should be interpreted with care due to substantial uncertainties in the estimates, and the differences in the scale of values of the events compared.

Implementation of the German Mammography Screening Program (German MSP) and First Results for Initial Examinations, 2005-2009

BACKGROUND

The German Mammography Screening Program (German MSP) is population-based and intended for women aged 50-69 years (approximately 10.5 million). The program started in 2005 and was implemented within 5 years. This article describes the implementation, structure, and screening process, and presents the results of initial examinations for the prevalence phase.

METHODS

Data were collected annually from invitation centers (invitation, attendance), screening units (performance, outcomes), and cancer registries (incidence).

RESULTS

In 2009, 92% of all annually eligible women were invited; 50% of the annually eligible population participated. The total cancer detection rate in the period of 2005-2009 was 8.1/1,000; the corresponding recall rate was 5.9%. 19.6% of detected cancers were ductal carcinoma in situ; 76.7% of invasive cancers were ≤ 20 mm in size, 30.2% were ≤ 10 mm, and 75.3% were node-negative. During the implementation period, incidence increased by 37 and 56% in the old and new federal states, respectively. Incidence rates decreased following the prevalence phase.

CONCLUSION

The German MSP was successfully implemented. The results of the prevalence phase meet the target values of the European guidelines. Proper functioning of the program is also verified by its effects on breast cancer incidence. To draw reliable conclusions regarding the long-term effects of the program, results from the routine screening rounds have to be awaited.

Breast cancer incidence and menopausal hormone therapy in Norway from 2004 to 2009: a register-based cohort study

In Norway, the breast cancer incidence increased by 50% in the 1990s, during a period with initiation of mammography screening as well as a fourfold increase in use of menopausal hormone therapy (HT). After 2002, the HT use has dropped substantially; however, the breast cancer incidence has declined only marginally. How much mammography screening contributed to the breast cancer incidence increase in the 1990s compared with HT use and specifically different types of HT use, has thus been discussed. Whether HT affects the incidence of subtypes of breast cancer differently has also been questioned. We have linked individual data from several national registries from 2004 to 2009 on 449,717 women aged 50–65 years. 4597 cases of invasive cancer and 681 cases of ductal carcinoma in situ (DCIS) were included in the analysis. We used Cox regression to estimate hazard ratio (HR) as a measure of the relative risk of breast cancer associated with use of HT. The HRs associated with prescriptions of HT for more than 1 year were 2.06 (1.90–2.24) for estrogen and progesterone combinations, 1.03 (0.85–1.25) for systemic estrogens, and 1.23 (1.01–1.51) for tibolone. Invasive lobular carcinoma was more strongly associated with use of estrogen and progesterone combinations, HR = 3.10 (2.51–3.81), than nonlobular carcinoma, HR = 1.94 (1.78–2.12). The corresponding value for DCIS was 1.61 (1.28–2.02). We estimated the population attributable fraction to 8.2%, corresponding to 90 breast cancer cases in 2006 indicating that HT use still caused a major number of breast cancer cases.

The contribution of mammography screening to breast cancer incidence trends in the United States: an updated age-period-cohort model

BACKGROUND

The impact of screening mammography on breast cancer incidence is difficult to disentangle from cohort- and age-related effects on incidence.

METHODS

We developed an age-period-cohort model of ductal carcinoma in situ (DCIS) and invasive breast cancer incidence in U.S. females using cancer registry data. Five functions were included in the model to estimate stage-specific effects for age, premenopausal birth cohorts, postmenopausal birth cohorts, period (for all years of diagnosis), and a mammography period effect limited to women ages ≥ 40 years after 1982. Incidence with and without the mammography period effect was calculated.

RESULTS

More recent birth cohorts have elevated underlying risk compared with earlier cohorts for both pre- and postmenopausal women. Comparing models with and without the mammography period effect showed that overall breast cancer incidence would have been 23.1% lower in the absence of mammography in 2010 (95% confidence intervals, 18.8-27.4), including 14.7% (9.5-19.3) lower for invasive breast cancer and 54.5% (47.4-59.6) lower for DCIS. Incidence of distant-staged breast cancer in 2010 would have been 29.0% (13.1-48.1) greater in the absence of mammography screening.

CONCLUSIONS

Mammography contributes to markedly elevated rates of DCIS and early-stage invasive cancers, but also contributes to substantial reductions in the incidence of metastatic breast cancer.

IMPACT

Mammography is an important tool for reducing the burden of breast cancer, but future work is needed to identify risk factors accounting for increasing underlying incidence and to distinguish between indolent and potentially lethal early-stage breast cancers that are detected via mammography.

Temporal changes in breast cancer incidence in South Asian women

BACKGROUND

Breast cancer in the UK resident population of South Asian ethnicity has been lower than that in indigenous women. Leicester has a large South Asian population and a breast cancer unit with comprehensive data on diagnosed cancers. This study analysed the annual incidence of new breast cancer diagnoses in females from 1998 to 2009 to determine any changes in recent years.

METHODS

Ethnicity was known in over 98% of cases. Population denominators were based on published figures for 2001 and 2011, projected back to 1998. Age-adjusted directly standardised incidence rates were determined by ethnicity and broken down by invasive status and screening classification. Incidence rates were analysed using logistic regression in order to identify statistically significant effects of age, ethnicity, deprivation and year of diagnosis. Interactions with invasive status and screening classification were also investigated.

RESULTS

At the start of the study period South Asian incidence was estimated to be 45% of that of the white population (p<0.001); by the end of the period the difference was still significant (p=0.022) but smaller, at 17%.

CONCLUSION

South Asians should no longer be considered at low risk of breast cancer.

Modern mammography screening and breast cancer mortality: population study

OBJECTIVE

To evaluate the effectiveness of contemporary mammography screening using individual information about screening history and breast cancer mortality from public screening programmes.

DESIGN

Prospective cohort study of Norwegian women who were followed between 1986 and 2009. Within that period (1995-2005), a national mammography screening programme was gradually implemented, with biennial invitations sent to women aged 50-69 years.

PARTICIPANTS

All Norwegian women aged 50-79 between 1986 and 2009.

MAIN OUTCOME MEASURES

Multiple Poisson regression analysis was used to estimate breast cancer mortality rate ratios comparing women who were invited to screening (intention to screen) with women who were not invited, with a clear distinction between cases of breast cancer diagnosed before (without potential for screening effect) and after (with potential for screening effect) the first invitation for screening. We took competing causes of death into account by censoring women from further follow-up who died from other causes. Based on the observed mortality reduction combined with the all cause and breast cancer specific mortality in Norway in 2009, we used the CISNET (Cancer Intervention and Surveillance Modeling Network) Stanford simulation model to estimate how many women would need to be invited to biennial mammography screening in the age group 50-69 years to prevent one breast cancer death during their lifetime.

RESULTS

During 15 193 034 person years of observation (1986-2009), deaths from breast cancer occurred in 1175 women with a diagnosis after being invited to screening and 8996 women who had not been invited before diagnosis. After adjustment for age, birth cohort, county of residence, and national trends in deaths from breast cancer, the mortality rate ratio associated with being invited to mammography screening was 0.72 (95% confidence interval 0.64 to 0.79). To prevent one death from breast cancer, 368 (95% confidence interval 266 to 508) women would need to be invited to screening.

CONCLUSION

Invitation to modern mammography screening may reduce deaths from breast cancer by about 28%.

Cancer incidence and mortality in France over the 1980-2012 period: solid tumors

BACKGROUND

Cancer incidence and mortality estimates for 19 cancers (among solid tumors) are presented for France between 1980 and 2012.

METHODS

Incidence data were collected from 21 local registries and correspond to invasive cancers diagnosed between 1975 and 2009. Mortality data for the same period were provided by the Institut national de la santé et de la recherche médicale. The national incidence estimates were based on the use of mortality as a correlate of incidence. The observed incidence and mortality data were modeled using an age-period-cohort model. The numbers of incident cases and deaths for 2010-2012 are the result of short-term projections.

RESULTS

In 2012, the study estimated that 355,000 new cases of cancer (excluding non-melanoma skin cancer) and 148,000 deaths from cancer occurred in France. The incidence trend was not linear over the study period. After a constant increase from 1980 onwards, the incidence of cancer in men declined between 2005 and 2012. This recent decrease is largely related to the reduction in the incidence of prostate cancer. In women, the rates stabilized, mainly due to a change in breast cancer incidence. Mortality from most cancer types declined over the study period. A combined analysis of incidence and mortality by cancer site distinguished cancers with declining incidence and mortality (e.g., stomach) and cancers with increasing incidence and mortality (e.g., lung cancer in women). Some other cancers had rising incidence but declining mortality (e.g., thyroid).

CONCLUSION

This study reveals recent changes in cancer incidence trends, particularly regarding breast and prostate cancers.

Trends in breast cancer stage distribution before, during and after introduction of a screening programme in Norway

BACKGROUND

Screening is intended to advance diagnosis thereby shifting the stage distribution towards more locally confined stages. Consequently we aimed to estimate trends in stage-specific breast cancer in relation to the introduction of population-based screening.

METHODS

From the Cancer Registry of Norway we retrieved cancer stage, age and year of diagnosis on all women aged 20 or older diagnosed with breast cancer during the period 1987-2010 in Norway (approximate source population: 1.8 million). Three calendar-time periods were defined: before (1987-95), during (1996-2004), and after (2005-10) screening was introduced; and two age groups: women eligible for screening (50-69 years) or younger (20-49 years). Poisson regression was used to estimate the incidence of localized (stage I) and more advanced cancer (stages II+), respectively, and logistic regression to estimate the proportion of localized cancer.

RESULTS

The annual incidence of localized breast cancer among women aged 50-69 years rose from 63.9 per 100 000 before the introduction of screening to 141.2 afterwards, corresponding to a ratio of 2.21 (95% confidence interval: 2.10; 2.32). The incidence of more advanced cancers increased from 86.9 to 117.3 per 100 000 afterwards, corresponding to a 1.35 (1.29; 1.42)-fold increase. Advanced cancers also increased among younger women not eligible for screening, whereas their incidence of localized cancers remained nearly constant.

CONCLUSION

Incidence of localized breast cancer increased significantly among women aged 50-69 years old after introduction of screening, while the incidence of more advanced cancers was not reduced in the same period when compared to the younger unscreened age group.

Systematic review about breast cancer incidence in relation to hormone replacement therapy use

BACKGROUND

Several studies report a decrease in breast cancer incidence subsequent to the decrease in hormone replacement therapy (HRT) use. But its magnitude and the time-lag may vary between countries. This may reflect differences in populations, previous type and prevalence of HRT use and breast cancer screening.

AIM

To review systematically studies assessing the relation between breast cancer incidence and change of HRT use.

MATERIAL AND METHOD

Descriptive analysis of the methodology of the studies including design limitations and presence of confounding factors, data sources for breast cancer and HRT and regimens of HRT used.

RESULTS AND DISCUSSION

Eighteen articles were selected. Most studies were ecological and confounding factors such as mammography screening and changes in reproductive and lifestyle habits could not be excluded. Sources of data on breast cancer and HRT were heterogeneous and only few data on HRT regimens used were available. Most studies concluded that the decrease in HRT use during the last decade was probably associated with a decrease in breast cancer incidence, especially for women aged 50 years or more.

CONCLUSIONS

Data, mostly from epidemiological studies, suggest that the decrease in breast cancer incidence can be partly attributed to the drop in HRT use. Nevertheless, available studies are hampered by a number of limitations and it remains difficult to evaluate the exact impact of the drop in HRT use on the decrease in breast cancer incidence. Especially, the studies are seldom based on detailed individual data and do not provide information on regimens used, type of cancers and possible confounding factors.

Overdiagnosis among women attending a population-based mammography screening program

Increased incidence of ductal carcinoma in situ (DCIS) and invasive breast cancer (IBC) after introduction of organized screening has prompted debate about overdiagnosis. The aim was to examine the excess in incidence of DCIS and IBC during the screening period and the deficit after women left the program, and thereby to estimate the proportion of overdiagnosis. Women invited to the Norwegian Breast Cancer Screening Program were analyzed for DCIS or IBC during the period 1995-2009. Incidence rate ratios (IRRs) were calculated for attended vs. never attended women. The IRRs were adjusted by Mantel-Haenszel (MH) method and applied to a set of reference rates and a reference population to estimate the proportion of overdiagnosis during the women's lifespan after the age of 50 years. A total of 702,131 women were invited to the program. An excess of DCIS and IBC was observed among women who attended screening during the screening period; prevalently invited women aged 50-51 years had a MH IRR of 1.86 (95% CI 1.65-2.09) and subsequently invited women aged 52-69 years had a MH IRR of 1.56 (95% CI 1.45-1.68). In women aged 70-79 years, a deficit of 30% (MH IRR 0.70, 95% CI 0.62-0.80) was observed 1-10 years after they left the screening program. The estimated proportion of overdiagnosis varied from 10 to 20% depending on outcome and whether the women were invited or actually screened. The results highlight the need for individual data with longitudinal screening history and long-term follow-up as a basis for estimating overdiagnosis.

Breast cancer mortality in Norway after the introduction of mammography screening

An organized mammography screening program was gradually implemented in Norway during the period 1996-2004. Norwegian authorities have initiated an evaluation of the program. Our study focused on breast cancer mortality. Using Poisson regression, we compared the change in breast cancer mortality from before to during screening in four counties starting the program early controlling for change in breast cancer mortality during the same time in counties starting the program late. A follow-up model included death in all breast cancers diagnosed during the follow-up period. An evaluation model included only breast cancers diagnosed in ages where screening was offered. The study group had been invited for screening one to three times and followed for on average of 5.9 years. In the follow-up model, 314 breast cancer deaths were observed in the study group, and 523, 404 and 638, respectively, in the four control groups. The ratio between the changes in breast cancer mortality between early and late starting counties was 0.93 (95% confidence interval [CI] 0.77-1.12). In the evaluation model, this ratio was 0.89 (95% CI: 0.71-1.12). In Norway, where 40% of women used regular mammography prior to the program, the implementation of the organized mammography screening program was associated with a statistically nonsignificant decrease in breast cancer mortality of around 11%.