NTRK1 and thyroid gland papillary carcinoma: Studies from our laboratory and from other groups have helped to identify the molecular events involved in thyroid carcinogenesis, i.e., activation of the RET/PTC and of the TrkA tyrosine kinase receptors in papillary carcinomas, activation of the ras genes by point mutation and PPARγ inactivation by fusion with PAX 8 in follicular carcinomas (Kroll et al, 2000), and mutation of the p53 gene in anaplastic tumours (Pierotti et al, 1996; Fusco and Santoro, 1997).