However, TR1 has also been implicated in tumor development and maintenance: 1) it is overexpressed in many tumors and cell lines [9]–[12]; 2) several antitumor drugs are potent inhibitors of TR1 suggesting that this enzyme is a target for cancer therapy [9]–[14]; 3) the targeted removal of TR1 reverses morphology and other cancer characteristics of malignant cells [16] (see also Figs. 2 and 3 and Text S1); and 4) selenium deficiency has been reported to decrease tumor formation is some cancer models in animals [24]. The gene discussed is TXNRD1; the disease is selenium deficiency.