Pancreatic cancer is one of the most common causes of cancer death in the United States. Unlike ω-3 fatty acids, which have been commonly used as complementary therapy to treat pancreatic cancer, ω-6s (more abundant fatty acids in the human diet) have received much less attention in cancer treatment due to generation of deleterious metabolites from cyclooxygenase (COX)-catalyzed peroxidation of arachidonic acid, a downstream ω-6. However, dihomo-γ-linolenic acid (DGLA), the immediate precursor of arachidonic acid, has been recently reported to be associated with some anti-cancer effects on various types of cancer cells. Recent studies from Dr. Qian’s lab have shown that the exclusive free radical byproduct 8-hydroxyoctanoic acid (8-HOA) formed from DGLA peroxidation catalyzed by COX-2 may actually account for DGLA’s anti-cancer activities. However, the generation of 8-HOA can be readily limited by the conversion from DGLA to arachidonic acid mediated by delta-5 desaturase (D5D). Here, we hypothesized that the high COX-2 expression in cancer cells and tumors can be exploited to promote formation of 8-HOA from COX-catalyzed DGLA peroxidation, and knockdown of D5D can reserve more DGLA to form 8-HOA which thus inhibits pancreatic cancer cell growth and migration. Clonogenic assay, apoptosis assay, transwell assay, immunofluorescence, and western blot were used to assess cancer cell and tumor viability, apoptosis, migration, invasion, and the associated molecular mechanisms. Our study showed that 8-HOA can inhibit pancreatic cancer cell growth and migration by acting as a histone deacetylase inhibitor to alter the expression of proteins involved in cancer growth and metastasis. We observed that knockdown of D5D (via siRNA/shRNA transfection) can promote formation of 8-HOA from COX-catalyzed DGLA peroxidation to a threshold level, leading to inhibition of pancreatic cancer cell growth and migration as well as subcutaneous tumor xenografts. Knockdown of D5D and DGLA treatment improved the efficacy of many chemotherapy drugs. We demonstrated that we could take advantage of the commonly overexpressed COX-2 level in cancers to control pancreatic cancer cell and tumor growth and metastasis. With this shifting paradigm of COX-2 biology in cancer treatment, the research outcome may provide us a ω-6s-based diet care strategy to supplement current chemotherapy.