FLT1 and thyroid gland undifferentiated (anaplastic) carcinoma: Previous studies proved FOXK2 induced apatinib resistance through VEGFA/VEGFR1 pathway in anaplastic thyroid cancer [15] and mutation of WRN induced apatinib resistance through activating the PI3K/AKT apoptosis-inhibiting pathway in non-small cell lung cancer [16].