Abstract
BackgroundWe 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.MethodsPopulation-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.ResultsOverall, 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.ConclusionsFuture incidence and survival reporting should be monitored by molecular subtypes to inform clinical planning and cancer control programmes.
Highlights
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
We report on breast cancer incidence trends in Scotland by ER and ER/human epidermal growth factor receptor 2 (HER2) combinations using several statistical methods: (1) age-standardised and age-specific incidence rates, which are typically used to report cancer statistics,[21] (2) joinpoint regression models to determine whether significant changes occurred during 1997–2016, and the speed at which they have occurred[22] and (3) age–period–cohort (APC) models[23,24,25] based on generalised linear model theory to enable description of age, period and birth cohort effects to provide possible clues to potential underlying factors contributing to incidence trends, and thereby inform public health and NHS programmes
Proportions with unknown ER status differed by region and age: higher in the West compared with the North and Southeast of Scotland and in women aged 70 years or older compared with women younger than 70 years (14% missing vs. 5%)
Summary
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. Age-standardised rates (ASR) and age-specific incidence were estimated by tumour subtype after imputing the 8% of missing oestrogen receptor (ER) status. Breast cancer incidence is rising and it is the most common cancer among women worldwide.[1] Breast cancer is not a single disease, but comprises multiple subtypes, with oestrogen receptor (ER) expression, a key marker of prognostic and aetiologic significance.[2] ER+ tumours, which are amenable to targeted antioestrogenic therapies, such as tamoxifen and aromatase inhibitors, are the most common type of breast cancers accounting for 65–75% of breast cancer cases in high-income populations.[3] Progesterone receptor (PR) is a commonly tested marker of hormone responsiveness that is highly correlated with ER. In addition to prognostic differences, epidemiologic studies have shown aetiologic differences by tumour subtypes.[5,6]
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