The influence of mammographic screening on national trends in breast cancer incidence

Rate of over-diagnosis of breast cancer 15 years after end of Malmö mammographic screening trial: follow-up study

OBJECTIVE

To evaluate the rate of over-diagnosis of breast cancer 15 years after the end of the Malmö mammographic screening trial.

DESIGN

Follow-up study.

SETTING

Malmö, Sweden.

SUBJECTS

42 283 women aged 45-69 years at randomisation.

INTERVENTIONS

Screening for breast cancer with mammography or not (controls). Screening was offered at the end of the randomisation design to both groups aged 45-54 at randomisation but not to groups aged 55-69 at randomisation.

MAIN OUTCOME MEASURES

Rate of over-diagnosis of breast cancer (in situ and invasive), calculated as incidence in the invited and control groups, during period of randomised design (period 1), during period after randomised design ended (period 2), and at end of follow-up.

RESULTS

In women aged 55-69 years at randomisation the relative rates of over-diagnosis of breast cancer (95% confidence intervals) were 1.32 (1.14 to 1.53) for period 1, 0.92 (0.79 to 1.06) for period 2, and 1.10 (0.99 to 1.22) at the end of follow-up.

CONCLUSION

Conclusions on over-diagnosis of breast cancer in the Malmö mammographic screening trial can be drawn mainly for women aged 55-69 years at randomisation whose control groups were never screened. Fifteen years after the trial ended the rate of over-diagnosis of breast cancer was 10% in this age group.

Population-based study of changing breast cancer risk in Icelandic BRCA2 mutation carriers, 1920-2000

BACKGROUND

Mutations in the BRCA genes increase the risk of breast cancer. Valid estimates of the magnitude of the lifetime risk of breast cancer in BRCA gene mutation carriers are needed for genetic counseling. Recent results suggest that penetrance has increased in recent birth cohorts. We examined the cumulative breast cancer incidence and mortality before age 70 over a diagnosis period of 80 years in Icelandic women who carried the BRCA2 founder mutation 999del5.

METHODS

Information on all breast cancers diagnosed in Iceland since 1911 was obtained from the Icelandic Cancer Registry. Mutation status was determined by molecular analysis of tissue samples for 847 breast cancer probands who were diagnosed from 1921 through 1985 and selected without knowledge of family history of breast cancer. We estimated the cumulative incidence and mortality from breast cancer before age 70 years in BRCA2 mutation carriers from the observed risks in first-degree relatives who were classified according to mutation status of probands and followed-up through 2002. Poisson modeling of these risks was also carried out. All statistical tests were two-sided.

RESULTS

Of the 847 probands, 88 carried the BRCA2 999del5 mutation and 759 did not. According to Poisson modeling, the cumulative incidence of breast cancer before age 70 years in mutation carriers increased from 18.6% (95% CI = 11.0% to 29.5%) in calendar year 1920 to 71.9% (95% CI = 45.9% to 100%) in 2002 (P < .001); in relatives of probands who did not carry the BRCA2 mutation and in the general Icelandic population incidence increased over the same period from 2.6% to 10.7% and from 1.8% to 7.5%, respectively (all increases of approximately fourfold). During the same period, the cumulative risk of death from breast cancer before age 70 years for BRCA2 mutation carriers increased from 12.1% (95% CI = 5.3% to 23.9%) to 26.9% (95% CI = 10.9% to 55.5%) (P = .08). However, because the probands were breast cancer patients and not a random sample from the population, some bias in the estimation of time trends in penetrance cannot be ruled out.

CONCLUSIONS

The results indicate that the penetrance of the Icelandic BRCA2 founder mutation increased nearly fourfold in 80 years, whereas the risk of death from breast cancer before age 70 years increased only approximately twofold. Changes in penetrance with time should be considered when penetrance is estimated.

Estimate of overdiagnosis of breast cancer due to mammography after adjustment for lead time. A service screening study in Italy

INTRODUCTION

Excess of incidence rates is the expected consequence of service screening. The aim of this paper is to estimate the quota attributable to overdiagnosis in the breast cancer screening programmes in Northern and Central Italy.

METHODS

All patients with breast cancer diagnosed between 50 and 74 years who were resident in screening areas in the six years before and five years after the start of the screening programme were included. We calculated a corrected-for-lead-time number of observed cases for each calendar year. The number of observed incident cases was reduced by the number of screen-detected cases in that year and incremented by the estimated number of screen-detected cases that would have arisen clinically in that year.

RESULTS

In total we included 13,519 and 13,999 breast cancer cases diagnosed in the pre-screening and screening years, respectively. In total, the excess ratio of observed to predicted in situ and invasive cases was 36.2%. After correction for lead time the excess ratio was 4.6% (95% confidence interval 2 to 7%) and for invasive cases only it was 3.2% (95% confidence interval 1 to 6%).

CONCLUSION

The remaining excess of cancers after individual correction for lead time was lower than 5%.

Effects of different phases of an invitational screening program on breast cancer incidence

The aim of this study was to quantify the effects of separate phases of an invitational screening program on breast cancer incidence at different ages. Our database included detailed municipality-specific information about invitations for mass-screening for breast cancer in 267 Finnish municipalities from time period 1987-2001. The age range was 50-74. For this study, the program was divided into 7 separate phases, and those that had not been invited served as a baseline. The incidence rate was modeled using Poisson regression. To study the differences between age groups within each program phase, an interaction term between age group and phase of screening was included in the model. The modeling was done separately for localized breast cancers, nonlocalized breast cancers and all stages combined. For localized cancers, the risk compared to the noninvited increased during the first years of the 2-year screening rounds in all age groups, and declined below the baseline during the second years. This effect was larger during the first round compared to the subsequent ones. In nonlocalized cancers, a clear incidence peak was detected only during the first year of the first round. A decreasing post screening effect was detected in nonlocalized cancers in women aged 60-69, but not in localized cancers. Cumulating over ages 50-74, extra incidence caused by regular screening in localized cancers was 5.2% if the program was continued up to age 59, and 28.0% if it continued up to age 69. Corresponding figures for nonlocalized cancers were decreases of 19.8% and 20.9%, respectively.

Predicting the future burden of cancer

As observations in the past do not necessarily hold into the future, predicting future cancer occurrence is fraught with uncertainty. Nevertheless, predictions can aid health planners in allocating resources and allow scientists to explore the consequence of interventions aimed at reducing the impact of cancer. Simple statistical models have been refined over the past few decades and often provide reasonable predictions when applied to recent trends. Intrinsic to their interpretation, however, is an understanding of the forces that drive time trends. We explain how and why cancer predictions are made, with examples to illustrate the concepts in practice.

Is there an association between SV40 contaminated polio vaccine and lymphoproliferative disorders? An age-period-cohort analysis on Norwegian data from 1953 to 1997

Between 1955 and 1963, an estimated number of 150 million people in various parts of the world, including Norway, received poliomyelitis vaccine possibly contaminated with infectious simian virus 40 (SV40). Human studies have investigated the hypothesised association between SV40 and various cancers, but the results have so far been contradicting. The aim of the present study was to examine Norwegian cancer incidence data to assess a possible association between birth cohorts assumed to have been subjected to the vaccine and the incidence rate of lymphoproliferative disorders (excluding Hodgkin's lymphoma), further subdivided into non-Hodgkin's lymphoma (NHL), lymphocytic leukemia and plasma cell neoplasms. Between 1953 and 1997, the incidence rate of lymphoproliferative diseases combined increased about 3-fold in both males and females. Subgroup analysis showed that this increase was largely attributable to NHL. Age-period-cohort modelling of the subgroups, as well as of all groups combined, showed that the cohort effect was more prominent than the period effect. However, the variations in incidence patterns across the birth cohorts did not fit with the trends that would be expected if a SV40 contaminated vaccine did play a causative role. Thus, our data do not support the hypothesis of an association between the vaccine and any subgroup of lymphoproliferative diseases.