RESUMO
INTRODUCTION: Genetic counseling and testing is recommended for women with a personal and/or family history of breast and other cancers (ovarian, pancreatic, male breast and others). Mutations in the BRCA1 and BRCA2 genes (BRCA1/2) are the most common causes of hereditary breast and ovarian cancer. Additional genetic counseling and testing with a multi-gene panel may be considered in breast cancer patients who tested negative for mutations in these two genes. In about 11% of BRCA1/2-negative patients, further genetic testing reveals pathogenic mutations in other high or moderate cancer risk genes. In 0.2% of cases, an individual may carry pathogenic mutations in more than one high penetrance gene (a double heterozygote). Finding one or more pathogenic mutations is important for cancer prevention in patients and/or their families. CASE PRESENTATION: Here we present a case of a breast cancer patient who did not have a pathogenic mutation in BRCA1/2 and had a family history of breast and stomach cancers. On an additional multi-gene panel testing, she was found to carry pathogenic mutations in the CDH1 and PMS2 genes, which cause Hereditary Diffuse Gastric Cancer and Lynch syndromes, respectively. To our knowledge, this is the first description of such a double heterozygote. DISCUSSION: Clinical manifestations, genetics, and management of both syndromes are reviewed, including prophylactic surgery and screening for unaffected family members. Management challenges for a mutation carrier with advanced breast cancer are discussed. Our case supports the clinical utility of additional multi-gene panel testing for breast cancer patients who do not have a pathogenic mutation in BRCA1/2 genes.