From the study of the PTC in The Cancer Genome Atlas (TCGA) cohort that excluded poorly differentiated and anaplastic thyroid cancers, alteration of the MAPK pathway was detected in 83% of all the tested PTC samples, with the mutually exclusive activating mutations in BRAF (62%) and RAS (13%), as well as RET/PTC rearrangement (6%), and less frequently NTRK3 fusion (1.5%), NTRK1 fusion (1.3%), and ALK fusion (0.8%) [19]. Here, NTRK1 is linked to thyroid gland undifferentiated (anaplastic) carcinoma.