Role of cancer associated adipocytes (CAA) and tumour associated collagen structures (TACS) in breast cancer cell invasion and metastasis

In post-menopausal breast cancer, obesity is related to invasive tumours that are resistant to chemotherapy and have a poor outcome. Recent research has revealed that adipocytes co-cultured with breast cancer cells (cancer-associated adipocytes or CAA) exhibit a decrease in late adipocyte differentiation markers, and increased expression of adipokines and extracellular matrix proteins such as collagen. In the breast tumour microenvironment collagen has been shown to exert a pro-tumorigenic influence by altering the tumour microenvironment to facilitate metastasis, and by acting as a ligand to stimulate breast cancer cells to undergo epithelial-mesenchymal transition (EMT). Therefore, the overall aim of this study was to investigate the role of the CAA-collagen axis in human breast carcinoma specimens. Specific objectives included (1) determining the number and size of CAA at the invasive margin and within the tumour, (2) identifying the patterns of collagen deposition and alignment near CAA and within the tumour, (3) determining the relative levels and localisation of markers of breast cancer cell EMT, and (4) analysing this experimental data together with tumour pathology and patient clinical data. The study cohort comprised 46 post-menopausal (aged 51yr+) women with invasive breast carcinoma, with formalin fixed paraffin embedded (FFPE) tumour samples and at least five years follow-up data available via the Cancer Society Tissue Bank Christchurch (CSTBC). Four patient groups were included: (1) Oestrogen receptor positive (ER+), Body Mass Index (BMI)=20-24.9 (n=11); (2) ER+, BMI>30 (n=12); (3) hormone receptor negative/triple negative breast cancer (TNBC), BMI=20-24.9 (n=10); and (4) TNBC, BMI >30 (n=13). The tumour samples were characterised by their clinicopathological parameters including histological subtype, Nottingham Prognostic Index (NPI), tumour size, tumour grade, lymph node status, stage and ER/PR/HER2 status. H&E stained tumour samples were assessed for the number and size of CAA along the interface and within the tumour, as well as the Tumour-Associated Collagen Signature (TACS) or pattern of collagen deposition and alignment, and these parameters were analysed together with patient clinicopathological data (Chapter 2). To investigate whether collagen was acting as a ligand to promote breast cancer cell metastasis, additional immunohistochemical analysis was used to determine the pattern of expression of Discoidin Domain Receptor 2 (DDR2) and markers of EMT (vimentin, Snail1) (Chapter 3). Experimental variables from both Chapters were analysed together with patient clinicopathological data including disease free survival and overall survival. Adipocyte diameter (p<0.001), area (p<0.001), and number (p=0.008) were all significantly decreased within the tumour compared to at the tumour interface. As expected, there was strong positive correlation between adipocyte diameter and area at both the interface and within the tumour (p<0.01), and both parameters were negatively correlated with adipocyte count (p