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 1997-2016 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 to 69 years, we observed an increase in ASR from 1997-2011 (1.6%/year, 95%CI: 1.2 to 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 to 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.