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

Abstract

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. ' 2005 Wiley-Liss, Inc.

Diagnostic work-up of contralateral breast cancers has not improved over calendar period

“…In the Stockholm cohort, mode of detection of the CBC was classified into four groups: (a) clinical work-up, which included CBCs detected through the follow-up program, by either mammography or palpation performed by health care personal, (b) self-palpation performed by the patient, (c) the national breast cancer screening program [10,18] For further analysis, we also constructed an alternative binary variable 'clinical work-up including mammography screening' (yes/no), which contrasts modes a ? c against b ?…”

Complexities in the estimation of overdiagnosis in breast cancer screening

“…The recent decline was mostly attributed to a lower prevalence of hormone replacement therapy (HRT) use (Ravdin et al, 2007), whereas the levelling off of screening mammography rates in the late 1990s has been suggested as contributing (Glass et al, 2007). In relation to increased incidence in the 1990s, this is usually attributed to the introduction of mammographic screening (Jonsson et al, 2005;Seppänen et al, 2006). It is well established that this causes an immediate rise in incidence, mainly due to the early diagnosis of a many prevalent asymptomatic cancers (Jonsson et al, 2005;Svendsen et al, 2006).…”

“…In relation to increased incidence in the 1990s, this is usually attributed to the introduction of mammographic screening (Jonsson et al, 2005;Seppänen et al, 2006). It is well established that this causes an immediate rise in incidence, mainly due to the early diagnosis of a many prevalent asymptomatic cancers (Jonsson et al, 2005;Svendsen et al, 2006). Also important is overdiagnosis, that is, the detection by screening of cancer which would never have been diagnosed in the host's lifetime if screening had not taken place Paci et al, 2006;Biesheuvel et al, 2007), estimated rates of overdiagnosis, ranging from around 3 to 50% or more (Biesheuvel et al, 2007).…”

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

“…[1][2][3][4][5][6][7][8][9][10] There is, however, a little information on how the separate phases of an invitational program differ from each other in terms of influencing the incidence. [1][2][3] It is also reasonable to assume that the impact of different program phases on breast cancer incidence is dependent on women's age and stage of cancer, which are issues that have, to our knowledge, never been studied jointly before.…”

“…1,2 In the study of Jonsson et al, starting times, age range and screening intervals of the included programs were collected by a questionnaire. 3 Our access to a database that includes actual year-and agespecific screening invitation information from Finnish municipalities makes it possible to take into account the real patterns of screening in the municipalities. It also makes it possible to study and code adequately the different phases of the 2-year massscreening cycle and to separate the years within a screening round from each other.…”