Investigating the role of the tumour microenvironment and E-cadherin in Invasive Lobular Carcinoma
Item statusRestricted Access
Embargo end date31/07/2022
Gómez Cuadrado, Laura
Invasive lobular carcinoma (ILC) is the second most common histological subtype of breast cancer after invasive ductal carcinoma (IDC), which account for 10-15% and 80% of diagnosed breast cancers, respectively. ILC is an understudied subtype of breast cancer that exhibits a number of clinico-pathological characteristics distinct from IDC. Histologically, ILC is characterized by small, discohesive cells which infiltrate in single files to surround normal breast structures, making diagnosis difficult due to the lack of a dense tumour mass. Molecularly, the hallmark of the lobular phenotype is the loss of E-cadherin expression. Clinically, ILC presents unique features, including an unusual pattern of metastatic dissemination, spreading to distinct sites such as the gastro-intestinal tract, peritoneum and ovary. Despite prognosis and survival rates being originally favourable, multivariate analysis has shown that patients with lobular histology appear to have a worse survival after a prolonged follow-up compared to patients with IDC. Despite these differences, ILC is treated in the same way as IDC. There is strong evidence supporting the importance of the tumour microenvironment (TME) in influencing tumour progression, metastatic spread and therapeutic response. However, little is known about the molecular mechanisms by which the TME influences the behaviour of ILC. We hypothesise that the interaction of ILC with the TME is critical for driving a disease distinct from IDC. Therefore, we sought out to identify alterations in the TME of ILC with potential clinical significance. This study is the first detailed analysis of the TME in ILC following laser-capture microdissection (LCM) of human ILC tissue samples to separate the tumour epithelium from the surrounding stroma. Analysis of our unique LCM-dataset, as well as the first gene expression analysis of cancer-associated fibroblasts (CAFs) from both ILC and IDC, demonstrate novel molecular differences in the TME between ILC and IDC, and identify genes that are enriched specifically in the stroma of ILC. One of these genes is PAPPA, which encodes pregnancy-associated plasma protein-A (PAPP-A), a secreted metalloproteinase that regulates the local bioavailability of IGF-1 and subsequent downstream signalling. We show that active PAPP-A is secreted from CAFs, and have identified it as the first gene to be a potential ILC prognostic marker following comprehensive survival analysis of large patient cohorts. This project also focused on the elucidation of the role of E-cadherin in breast cancer. E-cadherin is a transmembrane glycoprotein that enables cell-cell adhesion of epithelial cells. Despite solid knowledge about the loss of E-cadherin expression in ILC, not much is known about the implications for ILC biology. Hence, we have performed a variety of in vitro and in vivo studies to investigate the effect of E-cadherin loss in breast cancer cells. These studies conclude that loss of E-cadherin trigger intracellular changes that might contribute to the distinctive features of ILC. Interestingly, we found PAPPA to be significantly negatively correlated with CDH1 in breast cancer samples, which suggests a potential link between E-cadherin and PAPP-A. Taken together, the generation, analysis and validation of a series of novel datasets and other useful tools created during this PhD have enabled the elucidation of the role of the TME and E-cadherin in lobular breast cancer. In addition, these datasets will serve as valuable resources for other researchers in their studies.