To identify and quantify the functional tumor-stroma inter-relationships between tumor cells and cancer-associated fibroblasts (CAFs), a complex approach based on MALDI MSI and LC-MS/MS detected high levels of collagen 1 (COL1A) and alpha smooth muscle actin (α-SMA) in ER-negative BC patients with value of prognostic factors for cancer progression [108]. Here, ESR1 is linked to breast cancer.