In order to elucidate the factors contributing to intratumoral PGE2 levels, we evaluated the expression of COX-2/PGE2 pathway members MRP4, the prostaglandin transporter PGT, 15-PGDH (PGE2 metabolism), the prostaglandin E receptor EP4, COX-1, and COX-2 in normal, luminal, and basal breast cancer cell lines. Here, PTGS2 is linked to breast cancer.