Some studies found hypothyroidism may be the protective factor for cancers, as hypothyroidism can suppress tumor growth [32], in addition, Hercbergs et al. found that hypothyroidism could reduce the insulin-like growth factor 1, the antagonist of tamoxifen-induced cytotoxicity, to prolong the survival in recurrent high grade glioma patients [33]. Here, IGF1 is linked to central nervous system cancer.