Recent studies indicate that cyclooxygenase-2 (COX-2) is overexpressed in pancreatic adenocarcinoma and may play a critical role in this rapidly progressing form of cancer. A human pancreatic adenocarcinoma cell line, Mia PaCa-2, was incubated for 18 hours with 5 micromol/L of rofecoxib (Vioxx), a selective COX-2 inhibitor. Total RNA was isolated and gene expression analyzed by DNA microarray chips. In a separate experiment, athymic mice were orthotopically injected with 7.5 x 10(5) Mia PaCa-2 cells through a minilaparotomy. After 1 month, laparotomy was repeated to measure tumor size, and mice were randomized to receive reformulated rodent chow containing either 12.5 mg/kg/day of rofecoxib or no drug for 21 days. Tumor growth was assessed by comparing volume before and after treatment. In vitro, rofecoxib decreased gene expression of cyclin D1/PRAD1, a key component of cell cycle progression, while increasing expression of several cell cycle arrest genes, including p21/WAF1, p33/ING, GADD34, and GADD45 (P < 0.05). In vivo, tumor growth was significantly reduced in treated vs. control mice (P < 0.05). No systemic toxicity was observed in mice receiving rofecoxib. These data suggest that rofecoxib slows the growth of human pancreatic cancer through changes in gene expression that favor cell cycle arrest.