Combined treatment of γ-tocotrienol with PPARγ agonists increased COX-2, PGDS, and PGD2 synthesis, while combined treatment of γ-tocotrienol with PPARγ antagonists decreased COX-2, PGDS, and PGD2 synthesis in PPARγ siRNA transfected PPARγ positive MCF-7 and MDA-MB-231 breast cancer cells. The gene discussed is PTGS2; the disease is breast cancer.