Analysis of circulating tumor cell DNA, isolated from RET fusion-positive NSCLC or MTC patients who progressed after initial response to selpercatinib, revealed the emergence of three mutations: G810R, G810S, and G810C within the RET solvent front, which are predicted to sterically hinder binding of selpercatinib to RET fusions (277). The gene discussed is RET; the disease is medullary thyroid gland carcinoma.