RB1 and thyroid gland follicular carcinoma: Anaplastic thyroid carcinoma presents various subtypes: Type 1 BRAF-positive, with a genetic landscape similar to papillary thyroid carcinoma; Type 2 NRAS-positive which may originate from follicular thyroid carcinoma; Type 3 which carries RAS mutations or more atypical ones (e.g., PTEN, NF1 and RB1) and is likely to originate from Hürthle cell carcinoma; and Type 4 mixed, which harbor loss-of-function genetic alterations and mutations in the genes of cell-cycle regulations (CDKN2A and CDKN2B) [35].