Development in incidence of breast cancer in non‐screened danish women, 1973–2002—a population‐based study

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Abstract
The authors report on the incidence rates of breast cancer overall and by histology in a population of unscreened women constituting ∼80% of the total population of women in Denmark from 1973–2002, utilizing the files of the nationwide Danish Cancer Registry. The age‐specific incidence rates of breast cancer increased throughout the period, and further, marked changes in the age‐specific incidence pattern were observed, where the plateau and change of slope around the age of 46–48 in 1973–1981 shifted to around age 64–66 years in 1994–2002. Age‐period‐cohort modeling indicated that these changes were not attributable to a birth cohort effect. Although lobular breast cancer incidence increased more than ductal breast cancer incidence, this was only observed in the first decade after the introduction of the ICD‐O system in Denmark and probably is attributable to this, whereas we observed no disproportionate changes by histology in any age group from 1988–2002. Thus, previous reports of a disproportionate increase in lobular breast cancer could not be confirmed in a non‐screened population, whereas important changes over the past decade in the age‐specific incidence pattern of breast cancer particular around the time of menopause were indicated.