Biopsy material from the diagnostic endoscopy should be reviewed by an experienced histopathologist before discussion at the MDM to streamline decision making.

Environmental factors are important in causing gastric cancer (see section 1.2), and usually inherited factors (i.e. genes) play a minor role. Occasionally gastric cancers are due to an inherited cancer predisposition. The features that raise the possibility of an inherited cancer predisposition include:

• diffuse-type gastric cancer in people aged under 40 years
• Māori ancestry and diffuse-type gastric cancer at any age
• cleft lip or palate and diffuse-type gastric cancer at any age
• intestinal-type gastric cancer and a history of intestinal polyposis
• intestinal-type gastric cancer and multiple gastric fundic gland polyps in the absence of proton-pump inhibitor therapy
• personal history of another primary cancer, particularly colorectal, endometrial or lobular breast cancer
• family history of first- or second-degree relatives with primary gastric cancer (especially if diffuse-type), colorectal, endometrial or lobular breast cancer.

In some cases certain pathological subtypes of cancer or tumour tests (immunohistochemistry or tumour genetic tests) may suggest an underlying inherited cancer predisposition.

Anyone diagnosed with cancer should have a detailed personal and family cancer history taken. Consult relevant guidelines to determine if referral to a familial cancer service is appropriate.

A familial cancer service assessment can determine if genetic testing is appropriate. Genetic testing is likely to be offered when there is at least a 10 per cent chance of finding a causative ‘gene error’ (pathogenic gene variant; previously called a mutation). Usually testing begins with a variant search in a person who has had cancer (a diagnostic genetic test). If a pathogenic gene variant is identified, variant-specific testing is available to relatives to see if they have or have not inherited the familial gene variant (predictive genetic testing).

Medicare funds some genetic tests via a Medicare Benefits Schedule (MBS) item number but most are not. Depending on the personal and family history, the relevant state health system may fund public sector genetic testing.

Pre-test counselling and informed consent is required before any genetic testing. In some states the treating team can offer ‘mainstream’ diagnostic genetic testing, after which referral is made to a familial cancer service if a pathogenic gene variant is identified. The familial cancer service can provide risk management advice, facilitate family risk notification and arrange predictive genetic testing for the family.

Genetic testing is most likely to be helpful in the case of young onset or familial diffuse-type gastric cancer (see the eviQ website), especially when there is Māori ancestry (see table above). Genetic testing is not usually helpful when there is a personal or family history of intestinal-type gastric cancer only.

In most families with ‘gastric plus other cancers’, genetic testing is not able to identify a responsible gene. Notable exceptions include:

• a personal or family history of mismatch repair-deficient gastric (usually intestinal-type) cancer
• colorectal or endometrial cancer, which raises the possibility of lynch syndrome
• a personal or family history of intestinal-type gastric cancer and multiple colorectal adenomatous polyps, which raises the possibility of familial adenomatosis polyposis (FAP) and gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS).

Visit the Centre for Genetics Education website for basic information about cancer in a family.