Marked decreases of tumor volumes and weights were demonstrated in gemcitabine 160 mg/kg treated mice with decreases of the tumor cell volumes in the tumor masses were noticed, and also marked increases of the tumor mass caspase-3 and PARP immunoreactivities and decreases of COX-2 immunoreactivities were demonstrated in gemcitabine treated mice as compared with tumor-bearing control. This evidence concerns the gene PTGS2 and neoplasm.