A woman in her seventies presented with multiple polyps in her stomach, and a polyp in the lower gastric body was diagnosed pathologically as Group 4, borderline malignancy. Helicobacter pylori was eradicated as an alternative to gastrectomy, and the lesion disappeared morphologically and histologically 10 months after eradication. However, after 28 months, advanced gastric cancer suddenly appeared at a site different from that of the borderline malignancy lesion. Gastrectomy was performed, and the gastric cancer was diagnosed as a poorly differentiated adenocarcinoma. Most of the polyps were diagnosed as foveolar hyperplastic gastric polyps, but a few polyps were diagnosed as Peutz-Jeghers-type hamartomatous gastric polyps, which were histologically characterized by distinctive arborization of smooth muscle within the lamina propria. The patient was diagnosed with a solitary gastric Peutz-Jeghers-type polyp because she had Peutz-Jeghers-type hamartomatous polyps without family history, mucocutaneus pigmentation, and intestinal polyposis and did not meet the diagnostic criteria of Peutz-Jeghers syndrome. A solitary gastric Peutz-Jeghers-type polyp is very rare, and a high frequency of cancer complications has been reported; thus, careful observation for cancer screening is required.
