Recent trends in breast cancer incidence in Sweden

Abstract

Summary Breast cancer incidence in Sweden during the period shows no clear trend in women aged below 40 years but a transient increase at ages [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69] years, probably as a result of mammography screening. Our data give no indication that use of oral contraceptives or replacement hormones have affected nationwide breast cancer incidence rates. Keywords: breast cancer; incidence; trends The occurrence of breast cancer has been increasing worldwide in high-incidence Western countries as well as in low-incidence Asian countries (Quinn and Allen, 1995). Both in Scandinavia (Ewertz and Carstensen, 1988;Persson et al, 1993) (Chu et al, 1996). In a previous analysis of nation-based breast cancer incidence rates in Sweden during 1958-88, we found an average annual increase in the agestandardized rates of 1.3% (Persson et al, 1993). Although present in all age groups, this increase was most rapid among younger women. The rate of increase, however, slowed down towards the end of the study period, particularly among the youngest and oldest women. Birth cohort analyses revealed a more than twofold higher risk among women born in the 1940s compared with those born in the 1880s.A recent report from Norway -where there has been little mammographic screening -showed a substantial increase in breast cancer incidence during the period 1983-1993, which was confined to women aged below 50 years (Matheson and Tretli, 1996); the annual increases were 4.0%, 1.1% and 0.5% at ages 0-49, 50-59 and 60-69 years respectively. There was no evident change in the stage distribution over time. Correspondence to: Persson incidence that might be due to the implementation of mammography screening programmes in the late 1980s, to extensive use of combined oral contraceptives (COCs) in young women or to increasing use of hormone-replacement therapy (HRT) among post-menopausal women. SUBJECTS AND METHODSA nationwide cancer registry has operated in Sweden since 1958. In the majority of cases, the registry receives reports on diagnosed cancers from the responsible clinician as well as the pathologist or cytologist. Under-reporting of data to the registry has therefore been low, in the 1970s estimated at 5% (Mattsson and Wallgren, 1984) and in recent years at about 2% (Cancer Registry, 1996). For 98% of the breast cancer cases registered in 1993, the diagnosis was based on a histopathological examination; a similarly high figure was recorded during the last decade. In 1993 no cases were diagnosed at autopsy only (in previous years this figure was less than 0.6%).We based this updated analysis on all 50 022 cases of invasive breast cancer (ICD7 code 170) reported during a 10-year period from 1984 through 1993 (covering the last year with presently available statistics). The chosen period partly overlapped the previous study period and coincided, except for 1 year, with that of the Norwegian investigation (Matheson and Tretli, 1996). Statistical methodsWe analysed the trendwise deve...

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