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We read with interest the study by Tsukamoto et al. (2011) published in the recent issue of Asian Pacific Journal of Cancer Prevention. They examined the effect of the administration of long-term proton pump inhibitors (PPIs) to Mongolian gerbils (MGs) infected with Helicobacter pylori and observed the development of neuroendocrine tumors (NETs) and an increase in serum gastrin levels, but did not observe heterotopic proliferative glands (HPGs), gastritis, or any adenocarcinomas. In contrast, in our recent study, we observed atrophic corpus gastritis and the development of adenocarcinomas in an animal model (Hagiwara et al., 2011). Tsukamoto et al. cited our study and stated this difference may be due to differences in medicines or doses administered. However, we postulate that the differences between their experimental results and ours are caused by not only different medicines and doses administered but also the timing of initiation and duration of PPI administration. We were surprised that they did not detect any HPGs or corpus atrophic gastritis in the H. pylori-infected plus PPI-administered group. Several researchers have reported observing HPGs in the glandular stomach of MGs infected with H. pylori (Tatematsu et al., 2005), and we also observed HPGs and corpus atrophic gastritis in not only the H. pylori-infected group but also the H. pyloriinfected plus PPI-administered group in our recent study (Hagiwara et al., 2011). We speculate if H. pylori was eradicated or if their number was reduced significantly by lansoprazole administration in their study. Considering that PPIs are usually administered in adulthood, the timing of lansoprazole administration in their study, beginning one month after H. pylori infection, may be equivalent to that of lansoprazole administration in human infancy or childhood. The point of most concern in their study is that the authors have not evaluated the presence of infections. Moreover, they may have ignored another important fact that lansoprazole has stronger bacteriocidal activity against H. pylori than omeprazole; the MIC50 of lansoprazole is approximately 4-16 times lower than that of omeprazole (Midolo et al., 1996; Alarcon et al., 1998). These facts suggest that lansoprazole may have eradicated H. pylori in the early phase of their experiment before the establishment of H. pylori infection in the H. pylori-infected plus PPI-administered group in their study. Therefore, the timing of initiation of PPI administration may be important and should be set after considering LETTER to the EDITOR

asian pacific journal of cancer prevention

Experimental Strategies for Induction of Gastric Adenocarcinomas under Long-Term Proton Pump Inhibitor Administration and Helicobacter Pylori Infection