Simple Summary Cancer in the breast often spreads to other parts of the body, such as the lungs, which leads to poor outcomes for patients, as there are few effective treatments. Within organs such as the lungs, cancer cells are surrounded by a scaffold, made of proteins, which helps keeps the organs' structure and maintains their function. This scaffold is produced by cells called fibroblasts, and we can reproduce this in the lab. We aim to investigate how cancer cells interact with the protein scaffold from different organs, where breast cancer cells spread to. This study hopes to reveal how breast cancer reacts to different organ environments and use this method to perform large-scale drug screening. Importantly, this study has shown that drug testing of breast cancer cells within a more physiological context, as opposed to testing on plastic, can lead to increased identification of targets to treat breast cancer. During the metastatic process, breast cancer cells must come into contact with the extra-cellular matrix (ECM) at every step. The ECM provides both structural support and biochemical cues, and cell-ECM interactions can lead to changes in drug response. Here, we used fibroblast-derived ECM (FDM) to perform high throughput drug screening of 4T1 breast cancer cells on metastatic organ ECM (lung), and we see that drug response differs from treatment on plastic. The FDMs that we can produce from different organs are abundant in and contains a complex mixture of ECM proteins. We also show differences in ECM composition between the primary site and secondary organ sites. Furthermore, we show that global kinase signalling of 4T1 cells on the ECM is relatively unchanged between organs, while changes in signalling compared to plastic are significant. Our study highlights the importance of context when testing drug response in vitro, showing that consideration of the ECM is critically important.