Breast cancer is a heterogeneous disease and tumour markers help to predict prognosis and to drive treatment decisions. Unlike most cancer registries, since 2002 the National Cancer Registry has collected information about the three main breast cancer tumour markers: oestrogen receptor (ER), progesterone receptor (PgR) and human epidermal growth factor 2 (HER2). A quality assurance exercise was conducted to maximise the available information on these tumour markers. Following this, each breast cancer case has been classified by subtype: luminal A, luminal B, HER2 over expressing and triple negative.
The aim of this project was to investigate the epidemiology of different breast cancer subtypes at the population-level. The study has investigated:
(i) levels of testing for tumour markers and how this varies over time and across Ireland;
(ii) time trends in incidence of each subtype
(iii) patient-related and clinical characteristics of each subtype;
(iv) trends in treatment receipt by subtype; and
(v) survival by subtype.
A second stage of the project involved investigating prevalence and predictors (including subtype) of re-operation in women who initially underwent breast conserving surgery.