Hereditary Diffuse Gastric Cancer testing criteria have been established and are considered in families who meet any of the following criteria.
- Two or more cases of gastric cancer in first- or second-degree relatives, with at least one case confirmed to be diffuse gastric cancer
- One instance of diffuse gastric cancer diagnosed under age 40
- A personal or family history of both diffuse gastric cancer and lobular breast cancer, with one diagnosis under age 50
Also, families in whom testing could be considered are those who meet any of the following criteria.
- Bilateral lobular breast cancer or family history of two or more cases of lobular breast cancer under age 50
- A personal or family history of cleft lip/palate in a patient with diffuse gastric cancer
- In situ signet ring cells and pagetoid spread of signet ring cells
Affected patients from families meeting the criteria are referred for genetic counseling and testing for a CDH1 gene mutation. The genetic testing is performed in two stages, diagnostic testing, and predictive testing. Diagnostic testing is done using a blood sample from a patient affected with gastric cancer, to identify if a mutation in the CDH1 gene exists to cause cancer. If a mutation is identified, healthy family members who are at risk for inheriting the same mutation may choose to undergo predictive testing for the same mutation.
People from HDGC families are at an increased risk of developing diffuse-type gastric cancer and lobular breast cancer. It is estimated that the risk of developing gastric cancer by age 80 is 70% of men and 56% in women. Additionally, female carriers are at an increased risk (42% by age 80) for lobular breast cancer.