RESUMEN
BACKGROUND: Germline pathogenic variants in the cadherin-1 (CDH1) gene cause a predisposition to hereditary diffuse gastric cancer (HDGC). We report an HDGC case in Vietnam and identify a novel mutation in the CDH1 gene. CASE PRESENTATION: A 28-year-old Vietnamese man was diagnosed with HDGC and a novel mutation at c.639G>A. All exons of CDH1 were sequenced in his pedigree, which revealed the c.639G>A mutation in the proband, his father, and uncle. The patient refused treatment and died 4 months after diagnosis. Endoscopic surveillance of the father and the uncle showed structural abnormalities in the father. CONCLUSION: In cases of HDGC, identification of the CDH1 gene mutation is very important for better counseling and more effective strategies to prevent the development of diseases, such as prophylactic gastrectomy for family members with genetic mutations.