There is a 1 in 30 lifetime risk of bowel cancer with the prevalence being higher in men than women.

The majority of new cancers will be sporadic cases but 20% of new patients will have a family history of bowel cancer.

Approximately 6% will be due to the inheritance of an identifiable autosomal dominant faulty gene.

The two most common syndromes which predispose to bowel cancer are Lynch syndrome or hereditary non polyposis colon cancer (HNPCC) and familial adenomatous polyposis cancer (FAP).  In addition, there are a few rare syndromes.

Lynch syndrome (HNPCC)

This is the cause of bowel cancer in approximately 1 in 1500 people. Individuals who carry a mutation in one of the mismatch repair genes are at high risk of developing bowel cancer and this can occur at a young age (under 45yrs).

Colorectal cancer can occur when only a small number of polyps, or none at all, are present. Individuals who carry a mutation require two yearly colonoscopies from the age of 25yrs. With surveillance there is a mortality reduction of 65%.

HNPCC gene carriers are also at risk from a variety of other cancers including endometrial, ovary, stomach, urinary tract, small bowel and bile duct

FAP

1 in 8000 people have FAP.  Individuals who carry the gene for FAP may develop hundreds of pre-cancerous polyps by the second to third decade, and colorectal cancer is inevitable without a colectomy (approx 39yrs). 

Lower gastrointestinal (GI) screening is offered to individuals who carry the FAP gene from the age of 10yrs, and upper GI screening from the age of 30yrs. Following prophylactic colectomy, annual sigmoidoscopies are carried out on the residual rectal area. The FAP gene is associated with extra-colonic manifestations including gastric cancers, osteomas and desmoid disease.

Discussing risk and management with your patient

Using the familial bowel cancer referral guidelines it should be possible in most cases to determine whether your patient is at population (low) risk and can be managed in primary care or whether your patient’s risk may be raised and they would therefore benefit from referral. 

It may be helpful to consider what you might want to say to your patients in each of these situations and to discuss with them possible future management options.