To assess whether knockout of COX-2 affected lung tumorigenesis in mice carrying a K-ras allele (G12D) that spontaneously developed multifocal lung adenocarcinomas, we generated the K-ras/COX-2−/− mice by breeding female K-ras/COX-2+/− with male COX-2–null mice. The gene discussed is KRAS; the disease is lung adenocarcinoma.