We present the case of a 42-year-old female under study due to dyspepsia without response to empirical treatment, with perioral mucocutaneous pigmentation. A gastroscopy revealed a 5 cm gastric tumor in the antrum, as well as multiple sessile gastric and duodenal polyps smaller than 1 cm. Large-capacity forceps biopsies were obtained and a well-differentiated adenocarcinoma with gastric origin was diagnosed, with over expression of the HER2/neu without microsatellite instability in the context of a hamartomatous polyposis. The genomic study confirmed an alteration in the STK11 gene translated to a truncated protein product, compatible with a Peutz-Jeghers syndrome (PJS).