FLT1 and medullary thyroid gland carcinoma: Consistently, key angiogenic factors PDGFRB and VEGFR1 (FLT1) were also significantly upregulated in Mesenchymal tumors (Fig. 6f), which are not only drug targets for the FDA-approved tyrosine kinase inhibitor (TKI) cabozantinib, but also the targets of several other TKIs in clinical trials for advanced MTC such as sorafenib, lenvatinib, sunitinib, etc. (Supplementary Fig. S6e).