Gastric cancer is the fourth most commonly diagnosed malignancy and the second leading cause of cancer-related mortality worldwide. Recent research suggests that tissue stem cells and the self renewal transcription factor, octamer-binding transcription factor 4 (Oct4), could be involved in the development of certain tumors. The aim of this study was to investigate the expression pattern of Oct4 in normal human stomach and during multistep gastric carcinogenesis. Pyloric antral mucosal tissues were obtained from consenting individuals undergoing endoscopy (due to upper gastrointestinal symptoms) and gastrectomy (due to pyloric antral adenocarcinoma). Some tissue samples were processed to assemble an array of tissue sections representing multistep carcinogenesis and probed using anti-Oct4 antibodies and lectins specific for α-L-fucose or N-acetyl-D-glucosamine. Some tissue samples were processed for subcellular fractionation and western blot analysis using the same antibodies. The results revealed that Oct4-expressing cells were found in the proliferative cell compartment of the pit-gland units of microscopically normal gastric mucosal biopsies. Mucosal tissues with evidence of severe gastritis, metaplastic/dysplastic transformation and gastric cancer showed a significant increase in the expression of Oct4 (the labeled area increased from 2% in the control to 6 and 16% in the gastritis and cancerous tissues, respectively), suggesting a role for Oct4 in the early stages of cancer development. Furthermore, the data revealed an alteration in the subcellular distribution of Oct4, possibly due to the inhibition of cytoplasm-to-nucleus translocation during carcinogenesis. In conclusion, this study demonstrates an alteration in the expression pattern and nuclear translocation of Oct4 during gastric carcinogenesis and may be helpful in designing new modalities for the early detection and/or therapy of gastric cancer.