Genomics is becoming increasingly important in the treatment of cancer patients. Dr Sarah Taylor, GatewayC GP Lead, speaks to Dr Fiona Lalloo, Consultant Clinical Geneticist, about cancer genetics.

Key points:

• There are 2 types of genetic mutations:
  • Somatic mutations – these are mutations which are confined to the tumour and are useful to direct treatment
  • Germline mutations – these are mutations which affect every cell in the body. This can affect treatment but can also cause a predisposition to malignancies for the patient and members of their family
• Patients with germline mutations need referral to a genetics services. This is normally done by the oncology team but primary care practitioners may be asked to refer family members
• In that case it useful to know the name of the affected patient, the type of cancer and where they are being treated
• Many cancers are environmental but 5-10% of cancers have a germline mutation
• There are some cancer syndromes which have specific clusters of cancer types.

The National Genomic Test Directory lists the referral criteria for genetic testing for patients
who are concerned about a family history of cancer.

Factors which increase the probability of a germline mutation are:

• cancers occurring at young age
• individuals with more than one primary
• clusters of cancer within a family

Many cancers are environmental, but 5-10% of cancers have a germline mutation. There are some cancer syndromes which have specific clusters of cancer types.

Genomic testing in Wales

While the National Genomic Test Directory is owned, controlled and maintained by NHS England, the Welsh Health Specialised Services Committee (WHSSC) approve funding of genomic testing in line with the criteria identified in the Test Directory and implementation of these tests is being clinically prioritised in collaboration with a range of clinicians through the All Wales Medical Genomics Service.

Dr Fiona Lalloo discusses genetic syndromes associated with colorectal cancers.

Key points:

• There are a number of genetic conditions which pre-dispose to colorectal cancer including:
  • MUTYH (MYH)-associated polyposis (MAP)
  • Familial adenomatous polyposis (FAP) is a rare, inherited condition caused by a defect in the adenomatous polyposis coli (APC) gene
  • Lynch syndrome
• Lynch syndrome is the most common inherited syndrome associated with colorectal cancer. It is autosomal dominant
• 1 in 250 people carry the Lynch syndrome gene
• Every colorectal cancer should be screened for Lynch syndrome using immuno-histochemistry. Patients who have a positive screen will have germline testing
• Patients who are found to have Lynch syndrome will be put into a surveillance programme which normally includes 2 yearly colonoscopies from the age of 25. Women will have endometrial screening from age 35. BSG guidelines advise surveillance starts at the age of 25 or 35 based upon gene mutation
• Lynch screening has only been introduced in the last few years. It is worth considering referral in patients who have relatives who were diagnosed at a young age or where are there multiple family members involved
• The role of aspirin in preventing cancer in patients with Lynch syndrome is showing promising results.

Additional resources

Link: National Genomic Test Directory, NHS England
Link: All Wales Medical Genomics Service
Link: NCI Dictionary of Genetic Terms, National Cancer Institute
Link: NCI Dictionary of Cancer Terms, National Cancer Institute
Link: Inherited genes, Cancer Research UK 2018
Link: Testing strategies for Lynch syndrome, NICE diagnostics guidance (NICE DG12)
Link: Reducing risk of bowel cancer in people with Lynch syndrome, Cancer Research UK (2019)
Link: Guidelines for the management of hereditary colorectal cancer from the BSG/ACPGBI/UKCGG, The British Society of Gastroenterology (2019)
Link: European guidelines from the EHTG and ESCP for Lynch syndrome, The British Society of Gastroenterology (2021)