As rationale for the use of radiolabeled FAP-ligands in BC, it has been demonstrated that TME has a role in BC development, with the disease evolution depending not only on the intrinsic behavior of cancer cells (according to differences in gene expression patterns, hormonal receptor status, human epidermal growth factor receptor 2–HER2–expression, etc.), but also on TME composition and on the interactions between cancer cells and TME itself [15]. The gene discussed is ERBB2; the disease is breast cancer.