We present the case of a 38-year-old woman who, in the context of a 22-week gestation, was diagnosed with diffuse gastric adenocarcinoma. The age of the patient and the way in which the cancer presented itself, make genetic counseling mandatory to rule out hereditary diffuse gastric carcinoma syndrome. This rare entity, of autosomal dominant inheritance and closely linked to mutations in the CDH1 (in most cases) and CTNNA1 genes, is associated with a greater predisposition to develop malignant neoplasms of the breast and stomach. Genetic sequencing ruled out hereditary diffuse gastric cancer syndrome. Unfortunately, 24 months after the cesarean section, our patient dies.