Although STAT3 was previously reported for its effects to promote tumor cell survival and proliferation in the context of RET/PTC-tumorigenesis of NIH3T3 or TP53G199V signaling in an anaplastic thyroid cancer cell line [98,100], multiple studies have also identified STAT3 as a tumor suppressor in different thyroid cancer types. This evidence concerns the gene STAT3 and thyroid gland undifferentiated (anaplastic) carcinoma.