APC and breast carcinoma: Intriguingly, in a strain of Wnt-activated Apc+/1638N mice, TRα overexpression in the intestinal epithelium did not induce cancer formation but rather accelerated tumorigenesis.36 Recently, another group reported that TRs act as potent suppressors of tumor metastasis in breast cancer cell lines.37 The investigators further showed that mice with double knockout of TRα and TRβ are vulnerable to epithelial tumors and that TR deficiency suppresses the number of benign tumors but enhances malignant tumor formation during carcinogenesis.