Breast Cancer Res. 2006; 8(6): R68.
© 2006 Paci et al.; licensee BioMed Central Ltd.
Estimate of overdiagnosis of breast cancer due to mammography after adjustment for lead time. A service screening study in Italy
1Clinical and Descriptive Epidemiology Unit, CSPO, Research Institute of the Tuscany Region, via di San Salvi 12, Firenze, 50135, Italy
2ASL Bologna Area Nord, via Libertà 45, 40016, San Giorgio di Piano, Bologna, Italy
3U.O. Oncologia, Azienda Ospedaliera-Università, Parma Cancer Registry, via Abbeveratoia 4, Parma, 43100, Italy
4Dipartimento Interaziendale di Oncologia, Ospedale G.B. Morgagni–L. Pierantoni, Pad. Valsava, Romagna Cancer Registry, via C. Forlanini 34, Forlì, 47100, Italy
5Modena Cancer Registry, via del Pozzo 71, Modena 41100, Italy
6Ferrara Cancer Registry, Dipartimento di Medicina Sperimentale e Diagnostica, Sezione di Anatomia, Istologia e Citologia Patologica, Università di Ferrara, v. Fossato di Mortara 64B, Ferrara, 44100, Italy
7Epidemiology Unit, Reggio-Emilia Cancer Registry, via Amendola 2, Reggio-Emilia, 42100, Italy
8Screening Programme, Emilia-Romagna Region Health Department, viale Aldo Moro 21, 40127, Bologna, Italy
9CPO – Piedmont Cancer Registry, via San Francesco da Paola 31, Torino,10123, Italy
10CPO Piemonte, Epidemiology Unit, via San Francesco da Paola 31, Torino, 10123, Italy
11Umbria Cancer Registry, Dipartimento di specialità Medico-Chirurgiche e Sanità Pubblica, Università degli Studi di Perugia, via del Giochetto, Perugia, 06100, Italy
12Department of Oncology, ARNAS Ascoli, via Parlavechio 1, 90100, Palermo, Italy
13Department of Oncology 'Sebastiano Ferrara', Cancer Registry andUnit of Histopathology Azienda Ospedaliera 'Civile M.P. Arezzo', via Dante 109, Ragusa, 97100, Italy
14Dipartimento di Scienze oncologiche e chirurgiche, Università degli Studi di Padova, Istituto Oncologico Veneto (IOV), via Gattamelata 64, Padova, 35128, Italy
Received July 31, 2006; Revisions requested September 15, 2006; Revised October 13, 2006; Accepted December 5, 2006.
This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0
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In total we included 13,519 breast cancer cases diagnosed in the pre-screening years (corresponding to years from -5 to 0). In the five years of screening (years 1 to 5), 13,999 cases were included from the six cancer registries.
Pooling the pre-screening incidence data from the six areas, the annual percentage change in the pooled incidence trend was 1.2% (95% confidence interval (CI) 0.8 to 1.6) for all breast cancers and 0.9% (95% CI 0.5 to 1.3) for invasive breast cancers only.
Figure shows the excess of incidence observed in the study screening programmes for women aged 50 to 74 at diagnosis, over the screening time scale. Population-based incidence rates are presented by method of detection (not invited and invited, divided into screen detected and not screen detected). At the end of five years from time 0, 68.2% of the 50 to 74-year-old cases (77.7% of the cases aged 50 to 69 years) had received an invitation to be screened, and 37.5% (42.8% of the cases aged 50 to 69 years) were detected at screening.
Breast cancer incidence rates by method of detection, on the screening time scale. The participants were aged 50 to 74 years. SD, screen detected; NSD, not screen detected.
In Figure the incidence rates are presented by year relative to the start of screening and compared with the predicted rates in the absence of screening and with the data corrected for lead time. Results excluding in situ carcinomas were similar (data not shown).
Breast cancer incidence rates predicted, observed, and observed corrected for lead time. The participants were aged 50 to 74 years.
In Table the results are reported by 5-year age groups for women aged 50 to 74 years at diagnosis and compared with the predicted number of cases in the absence of screening. In total, in the first 5 years of screening, the ratio of observed to predicted in situ and invasive cases was 136.2% (95% CI 134 to 139%), a 36% excess of cases. After correction for lead time, the ratio for in situ and invasive cases was 104.6% (95% CI 102 to 107%), and for invasive cases only it was 103.2% (95% CI 101 to 106%).
Observed, predicted, screen-detected breast cancer cases and observed corrected-for-lead-time cases, by age group
In Figure the excess of breast cancer incidence is presented by 5-year age group at diagnosis, comparing incidence rates in the period 1 to 3 years since start (this is equivalent to the period of the first round of screening) and 4 to 5 years after the start (subsequent rounds), and incidence rates after the correction for lead time. The dotted line shows the predicted incidence rates in the absence of screening. The 50 to 54-year-old women showed an excess of 7.4% in both the first and subsequent rounds. Indeed, in the period 4 to 5 years after the start, women aged 50 to 54 years were mostly new entries (prevalent screening).
Breast cancer incidence rates by age group and years since the start of the screening.
In the following analysis, breast cancer incidence rates were estimated with a cohort approach grouped by age at the beginning of the screening programme. Women are aging over the screening time scale, so the predicted number of cases is expected to increase over time. In Figure results are presented by five year age group and compared with the predicted and the corrected-for-lead-time cases. With the cohort method, the observed rates corrected for lead time corresponded very closely to the predicted ones, particularly for the 55 to 64-year-old age group. Women aged 65 to 69 years showed an increase in incidence, reaching the highest of all groups' peaks at prevalence screening. Whereas some of them could have continued screening at older ages, we observed a sharp decrease in the incidence in women within the five year follow-up period. The incidence rate decreases close to the level of the expected incidence.
Breast cancer incidence rates predicted, observed, and observed corrected for lead time. The age groups at first invitation were as follows: (a) 50 to 54 years; (b) 55 to 59 years; (c) 60 to 64 years; (d) 65 to 69 years; (e) 70 to 74 years.