PPARD and cancer: Using heterozygous PPARβ/δ mice for syngenic tumor cell vein injection the authors further demonstrated that high expression of PPARβ/δ in cancer cells is the most important factor for metastasis formation as heterozygous PPARβ/δ mice developed fewer metastasis than their wildtype littermates, but exhibited the most important reduction of metastasis formation when injected with PPARβ/δ knockdown cancer cells.