In a series of 45 poorly differentiated adenocarcinomas (por) and 7 signet‐ring‐cell carcinomas (sig) of the colorectum, K‐ras gene mutation, p53 immunostaining and microsatellite instability (MSI) were analyzed for a comparison with 46 cases of colorectal carcinomas of the well or moderately differentiated type (well/mod). In addition, the mutations of simple repeated sequences in the transforming‐growth‐factor‐β type‐II receptor (T β R‐II) gene and the BAX gene were analyzed as possible targets for DNA replication errors. Mutation of the K‐ras gene in the por, sig and well/mod specimens was detected in, respectively, 22%, 11% and 48%, positive immunostaining for p53 in 41.8%, 28.6% and 60.3%, and MSI in 36%, 30% and 4%. Frameshift mutation of the T β R‐II gene was detected in 27.5% of the por and none of the sig specimens, while corresponding figures for mutation of the BAX gene were 15.7% and 0%. Significant differences between the por and well/mod tumors were found in the occurrence of K‐ras mutation at codons 12 and 13, and MSI. Clinicopathologically, the tumor status of por with MSI was found to significantly correlate with the tumor's location in the proximal colon. In cases without MSI and sig, no frameshift mutation of either the T β R‐II or the BAX gene was found. These results suggest that poorly differentiated and signet‐ring‐cell carcinomas have a genetic background different from that of well or moderately differentiated carcinomas of the colorectum, and that DNA‐replication error is at least partly involved in the carcinogenesis of these specific types of colorectal carcinomas. Int. J. Cancer (Pred. Oncol.) 84:33–38, 1999. © 1999 Wiley‐Liss, Inc.

Helicobacter pylori infection is associated with the development of gastric cancer. In short-term coculture with AGS gastric cells, H. pylori inhibits cell cycle progression and induces dose-dependent apoptosis. Based on the concept that an imbalance between proliferation and apoptosis may contribute to the emergence of gastric cancer, we chronically exposed AGS cells to H. pylori as a model of chronic exposure in humans. The AGS derivatives selected by this process were stably resistant not only to H. pylori-induced apoptosis but also to apoptosis induced by other enteric bacteria and by several toxic agents including radiation and cancer chemotherapy. Like the parental AGS cells, the derivatives underwent G 1 /S-phase cell cycle inhibition in response to H. pylori. The AGS derivatives displayed a marked decrease in cellular levels of the cell cycle control protein p27 kip1 . We found a similar decrease in epithelial cell p27 kip1 expression in gastric biopsy specimens from H. pylori-infected patients. These findings are consistent with observations that link decreases in the p27 kip1 level to increased susceptibility to cancer in mice with p27 kip1 deleted and to a poor prognosis of gastric cancer in humans. This is the first demonstration that bacterial infection can lead to apoptosis resistance and to cross-resistance to other inducers of apoptosis such as bacteria, chemotherapeutic agents, and radiation. The development of apoptosis resistance and downmodulation of p27 kip1 may contribute to the increased risk for gastric cancer observed in humans chronically exposed to H. pylori.

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