Mammography benefit in the Canadian National Breast Screening Study‐2: A model evaluation

Abstract

The CNBSS-2 among women aged 50 -59 did not show any significant difference in breast cancer mortality between a control arm screened annually by CBE and a study arm screened by CBE and mammography. Because of this design, the benefit of screening compared to no screening could not be evaluated. We therefore conducted a modeling effort to estimate the benefit of mammography or CBE compared to no screening. We incorporated demographic, epidemiologic and screening characteristics of the CNBSS-2 in MISCAN. Stage-specific sensitivities of CBE, with and without mammography, and breast cancer incidence rate in the trial were estimated by comparing observed trial data with model predictions. We predicted the number of breast cancer deaths for both study arms of the CNBSS-2 and in the absence of screening, assuming improvement in prognosis by early detection. We estimated a 24 -29% higher breast cancer incidence rate in the CNBSS-2 than the average Canadian rate. Key words: breast cancer; screening; mortality; mammography; clinical breast examination; Canadian National Breast Screening Study-2Several randomized controlled trials have assessed the efficacy of mammography screening at reducing breast cancer mortality. An updated overview of 4 Swedish randomized trials showed breast cancer mortality reductions in invited women of 16% (50 -59 years) and 33% (60 -69 years). 1 However, in a Cochrane review, the authors found smaller breast cancer mortality reductions in 2 so-called medium-quality trials. 2 The Malmö trial and the CNBSS-2 showed 20% (Ն55 years) and 3% (50 -59 years) breast cancer mortality reductions after 7 years of follow-up.The CNBSS-2, however, was designed to evaluate the efficacy of annual mammography over and above annual CBE. The 7-and 13-year follow-up results of this randomized trial did not show a significant difference in mortality from breast cancer between the 2 groups, even though high detection rates were found. 3,4 Because the control arm was screened, no estimations of mammography benefit compared to no screening could be made, as is available from other mammography trials, nor any estimate of the benefit of CBE screening.Here, we provide a quantitative interpretation of the CNBSS-2 results, using a MISCAN model evaluation of the trial. MISCAN is a microsimulation program, which has been successfully applied in the evaluation of different cancer-screening programs. [5][6][7] The main purpose of the model evaluation is to show what can be learned about breast cancer screening for women aged 50 and above and about the natural history of the disease from the CNBSS-2 in relation to what we know from other breast cancerscreening trials. The evaluation addresses 2 specific questions: (i) Can any explanations, resulting from the model evaluation, be given for the observed equal breast cancer mortality in both study arms of the CNBSS-2? (ii) What percentage of breast cancer mortality reduction by mammography screening compared to no screening can we estimate for the CNBSS-2? MATERIAL AND METHODS CNB...

Is Clinical Breast Examination Important for Breast Cancer Detection?

“…Mammography with cbe and bse detected cancers at an earlier stage than did cbe with bse, but no mortality benefit in women 50-59 years of age was observed 6 . A study by Rijnsburger et al 30 showed that cbe with bse should lower breast cancer mortality by 20% in women 50-59 years of age, but no adjustment was made for hormonal therapy and chemotherapy. In the province of Quebec, breast cancer screening with mammography has been offered to women 50-69 years of age since 1998, and that initiative could explain why our study shows that mammograms were more frequently positive in that age group.…”

Preventing breast cancer in LMICs via screening and/or early detection: The real and the surreal

“…In fact some of the earliest evidence regarding combining various screening modalities come from the breast screening trial set within the Health Insurance Plan of New York where mammography was combined with CBE and almost 70% effect was estimated to be due to CBE [64] . The Canadian Breast Screening Study among women aged 50-59 (CNBSS 2) found no benefit from adding mammography to CBE and BSE [65] , with around 20% mortality reduction achieved due to CBE and BSE [66] . The evidence regarding the usefulness of BSE is more indirect, with evidence observed in CNBSS 2 [66] .…”

Differences in Natural History between Breast Cancers in BRCA1 and BRCA2 Mutation Carriers and Effects of MRI Screening-MRISC, MARIBS, and Canadian Studies Combined

“…MISCAN is a well-validated microsimulation model used to evaluate various screening programs (21)(22)(23)(24). In MISCAN, individual life histories are simulated.…”

“…Mammographic sensitivities for premenopausal women (under 50 years) and MRI sensitivities were first estimated from the (largest) MRISC study. Stage-specific sensitivities of CBE in women 55 years or older were based on the Canadian National Breast Screening study (23). For women under 50 years, the CBE sensitivity was assumed to be 50% of the sensitivity for women >55 years.…”