Biological Characteristics of Older Women (> 70 Years) With ER Positive, HER2 Negative Early Breast Cancer

This study is investigating the biological characteristics of early oestrogen receptor (ER) positive, human epidermal growth factor receptor 2 (HER2) negative breast cancer (BC) in older woman (aged \> 70 years) who were treated with adjuvant endocrine treatment (ET). It will use surgical tissue previously collected as part of routine care from patients aged 70 years or older at diagnosis with ER positive, HER2 negative stage I-III BC treated The Royal Marsden NHS Foundation Trust (RMH). The overarching aim of this study is to define the biological characteristics of early BC in older women in terms of tumour microenvironment (TME), molecular and genomic features. This analysis will include assessment of tumour infiltrating lymphocytes (TILs), and gene expression profiling with NanoString using the Breast Cancer 360 (BC360TM) assay measuring ribonucleic acid (RNA) expression signatures of genes involved in proliferation, endothelial, angiogenesis, cytotoxicity, stroma, inflammatory chemokines, and apoptosis. This analysis will examine various biological pathways, aiming to inform suitability for certain treatments including cyclin-dependent kinase inhibitors (CDKi), chemotherapy, immunotherapy, or targeted treatments such as phosphoinositide 3-kinases (PI3K) inhibitors, or deoxyribonucleic acid (DNA) damage response.