Distinct temporal trends in breast cancer incidence from 1997 to 2016 by molecular subtypes: a population-based study of Scottish cancer registry data

BACKGROUND: We describe temporal trends in breast cancer incidence by molecular subtypes in Scotland because public health prevention programmes, diagnostic and therapeutic services are shaped by differences in tumour biology. METHODS: Population-based cancer registry data on 72,217 women diagnosed with incident primary breast cancer from 1997 to 2016 were analysed. Age-standardised rates (ASR) and age-specific incidence were estimated by tumour subtype after imputing the 8% of missing oestrogen receptor (ER) status. Joinpoint regression and age–period–cohort models were used to assess whether significant differences were observed in incidence trends by ER status. RESULTS: Overall, ER-positive tumour incidence increased by 0.4%/year (95% confidence interval (CI): −0.1, 1.0). Among routinely screened women aged 50–69 years, we observed an increase in ASR from 1997 to 2011 (1.6%/year, 95% CI: 1.2–2.1). ER-negative tumour incidence decreased among all ages by 2.5%/year (95% CI: −3.9 to −1.1%) over the study period. Compared with the 1941–1959 birth cohort, women born in 1912–1940 had lower incidence rate ratios (IRR) for ER+ tumours and women born in 1960–1986 had lower IRR for ER− tumours. CONCLUSIONS: Future incidence and survival reporting should be monitored by molecular subtypes to inform clinical planning and cancer control programmes.