However, the absence of complete inactivation of the gene [6] suggests that the germline mutation of the APC gene confers only a generic susceptibility to thyroid cancer [5–11], but perhaps other factors, namely, modifier genes, sex-related factors (hormonal, but also dietary, metabolic, and immunological), or environmental factors [31], are also required for the phenotypic expression. This evidence concerns the gene APC and thyroid cancer.