Occupational Factors and Socioeconomic Differences in Breast Cancer Risk and Stage at Diagnosis in Swiss Working Women

SIMPLE SUMMARY: Socioeconomic status and occupation affect the risk of breast cancer, the most common cancer in women, but whether the effect is the consequence of work exposure or of socioeconomic status is often difficult to understand. In a Swiss cohort study, these correlated factors were obtained at individual level. Controlling for socioeconomic status, women in high skill occupations and of high socioprofessional level were both at increased risk of breast cancer and at increased chance of an early diagnosis. This finding suggests that socioeconomic status and occupation both contribute to inequalities in breast cancer risk and early detection. Interdisciplinary studies with collection of biological, occupational and behavioural information are needed to further explain the causes of socioprofessional inequalities in risk and subtypes of breast cancer. ABSTRACT: Socioeconomic differences in breast cancer (BC) incidence are driven by differences in lifestyle, healthcare use and occupational exposure. Women of high socioeconomic status (SES) have a higher risk of BC, which is diagnosed at an earlier stage, than in low SES women. As the respective effects of occupation and SES remain unclear, we examined the relationships between occupation-related variables and BC incidence and stage when considering SES. Female residents of western Switzerland aged 18–65 years in the 1990 or 2000 census, with known occupation, were linked with records of five cancer registries to identify all primary invasive BC diagnosed between 1990 and 2014 in this region. Standardized incidence ratios (SIRs) were computed by occupation using general female population incidence rates, with correction for multiple comparisons. Associations between occupation factors and BC incidence and stage at diagnosis were analysed by negative binomial and multinomial logistic regression models, respectively. The cohort included 381,873 women-years and 8818 malignant BC, with a mean follow-up of 14.7 years. Compared with reference, three occupational groups predominantly associated with a high socioprofessional status had SIRs > 1: legal professionals (SIR = 1.68, 95%CI: 1.27–2.23), social science workers (SIR = 1.29; 95%CI: 1.12–1.49) and some office workers (SIR = 1.14; 95%CI: 1.09–1.20). Conversely, building caretakers and cleaners had a reduced incidence of BC (SIR = 0.69, 95%CI: 0.59–0.81). Gradients in BC risk with skill and socioprofessional levels persisted when accounting for SES. A higher incidence was generally associated with a higher probability of an early-stage BC. Occupation and SES may both contribute to differences in risk and stage at diagnosis of BC.