Do breast cancer risk factors differ among those who do and do not undertake mammography screening?

Objectives: There is considerable interest in whether mammography screening leads to over-diagnosis of breast cancer. However self-selection into screening programmes may lead to risk differences that affect estimates of over-diagnosis. This study compares the breast cancer risk profiles of participants and non-participants of population-based mammography screening. Risk profiles are also compared between those who have and have not used private screening services. Setting: This study involved 1162 women aged 40-84 who participated in the 2012 Health Omnibus, an annual face-to-face interview-based survey of a representative sample of the population in the state of South Australia. Methods: Data were collected on participation in mammography screening, demographic characteristics and breast cancer risk factors (including reproductive, familial and lifestyle factors). Missing data were multiply imputed. Factors independently associated with ever having been screened were identified using multivariable logistic regression, for population-based and ad hoc, private mammography screening separately. Results: Compared with non-participants, participants of population-based screening were more likely to have used hormone replacement therapy (odds ratio [OR] = 3.72), experienced breast biopsy or surgery (OR = 2.22), and be overweight or obese (OR = 1.57). They were less likely to be sufficiently active (OR = 0.57) or be born in a non-English speaking country (OR = 0.50) or aged under 50 (OR = 0.09). Women who were screened privately were more likely to have a family history of breast cancer (OR = 1.66) and have experienced breast biopsy or surgery (OR = 3.17) than those who had not. Conclusions: South Australian women who participated in the population-based mammography screening have a slightly higher prevalence of breast cancer risk factors. This also applies to those who undertook private screening.