Most bowel cancer is what doctors call sporadic — meaning it happens in people without a strong family history, often because of a combination of age, lifestyle and bad luck. Only around 5 to 10 in every 100 bowel cancers are caused by an inherited (or hereditary) genetic change — a fault passed down through families.
The two most common inherited bowel cancer syndromes are Lynch syndrome and familial adenomatous polyposis (FAP). There are several less common ones too. Recognising these syndromes matters because it changes how often you should be screened, when screening should start, and sometimes whether you should consider preventative (risk-reducing) surgery.
If you are reading this because a relative has been diagnosed and you are worried about your own family, please know that for most people the answer is reassuring — even if you do have a hereditary syndrome, regular screening is very effective at preventing cancer from developing in the first place.
Lynch syndrome (which used to be called HNPCC, or hereditary non-polyposis colorectal cancer) is the most common inherited bowel cancer condition. It is caused by a fault in one of the genes that normally repair small mistakes when your DNA copies itself — genes with names like MLH1, MSH2, MSH6, PMS2, and EPCAM.
If you have Lynch syndrome, your lifetime risk of bowel cancer is somewhere between 10% and 50%, depending on the specific gene involved (MSH6 and PMS2 sit at the lower end; MLH1 and MSH2 at the higher end). This is markedly higher than the general population's risk. There is also an increased risk of some other cancers, particularly cancer of the womb lining (endometrial cancer) in women, and less commonly cancers of the ovary, stomach, urinary tract and others. Cancers often occur at younger ages than in people without the syndrome.
The good news: regular surveillance colonoscopy is very effective at finding and removing polyps before they have a chance to become cancers.
FAP is caused by a fault in a gene called APC. People with FAP develop hundreds, sometimes thousands of small bowel polyps from their teenage years onwards. Without treatment, almost everyone with classic FAP will eventually develop bowel cancer — usually before age 40.
For this reason, people with FAP are usually offered a planned, preventative operation to remove most of the colon in late adolescence or early adulthood — well before any cancer forms. This is a big decision, but it is also a very effective one: it essentially prevents the cancer from ever occurring.
A milder form called attenuated FAP exists, with fewer polyps and a later onset, and is managed differently.
Another inherited cause of multiple polyps, this one needing a faulty copy of the MUTYH gene from both parents (whereas Lynch and FAP only need one). MAP can look a bit like attenuated FAP — multiple polyps, increased cancer risk — and is managed with similarly intensive surveillance.
There are several rarer syndromes that can also affect the bowel — names like Peutz–Jeghers syndrome, juvenile polyposis syndrome, Cowden syndrome (also called PTEN hamartoma tumour syndrome), and serrated polyposis syndrome. Each has its own pattern of polyps and its own screening recommendations. A family cancer specialist can identify these and advise you specifically.
Diagnosis combines three things: a careful family history (who, what cancer, what age), the pattern of polyps and cancers seen at colonoscopy, and genetic testing — a blood or saliva test that looks for specific gene faults.
If your family pattern suggests a syndrome — for example, several relatives affected, cancers diagnosed at young ages, multiple cancers in one person, or characteristic features like endometrial cancer alongside bowel cancer — your GP can refer you to a specialist surgeon and to a family cancer clinic for proper genetic counselling and testing.
Genetic counsellors are specialists in this area. They explain what testing can and cannot tell you, help you decide whether testing is right for you, and support you through the results. Testing is not something to take lightly — but it is also nothing to be afraid of, and the information can be very valuable.
If you are confirmed to have a hereditary syndrome — or you are an untested first-degree relative of someone who is — surveillance is much more intensive than the standard national screening program.
For Lynch syndrome: colonoscopy every 1–2 years starting around age 25. Women may also be offered surveillance for endometrial cancer, and risk-reducing removal of the uterus and ovaries can be discussed once family planning is complete.
For FAP: planned removal of the colon (a colectomy) in late adolescence or early adulthood, well before any cancer develops. The exact operation depends on the pattern of polyps.
For MAP and the rarer syndromes: surveillance is tailored to the specific syndrome and how it is behaving in your family.
Mr Nguyen works closely with family cancer clinics and genetic counsellors to coordinate surveillance and surgical management for patients with hereditary bowel cancer syndromes. He will explain what a positive test result means in practical terms, talk you through surveillance or risk-reducing surgery options, and support both you and your at-risk family members.
This is a long-term partnership, not a one-off conversation. The aim is to keep you well over many years.
Consider asking your GP about a family cancer clinic referral if you have: a first-degree relative diagnosed with bowel cancer before age 50; two or more first-degree or second-degree relatives with bowel cancer on the same side of the family; family members with multiple primary cancers (such as bowel and endometrial); a personal or family history of multiple bowel polyps; or a previously identified family genetic mutation.
Even if you are not sure whether your family pattern is significant, it is worth raising — your GP can help work it out.
Not everyone — only those whose family pattern suggests a syndrome. A family cancer clinic will look at who has been affected, at what age, and with what type of cancer, and decide whether testing is appropriate. For most people with a family history, the answer is more frequent colonoscopy rather than genetic testing.
No. Lynch syndrome raises your risk, but it is not a certainty — and the whole purpose of regular colonoscopy is to find and remove polyps before they have the chance to become cancerous. Most people with Lynch syndrome who follow their surveillance plan never develop bowel cancer.
If a hereditary syndrome is confirmed in you, first-degree relatives — including children — should be offered genetic counselling. Testing in children is usually deferred until late adolescence or early adulthood (the age depends on the syndrome and when surveillance would start). Genetic counsellors will guide you through this conversation.
This is a reasonable concern and worth discussing with a genetic counsellor before testing. In Australia, federal legislation has been passed to ban life insurers from using adverse genetic test results when deciding cover — the ban has no financial cap and commences in late 2026. A voluntary industry moratorium (covering policies up to $500,000) applies until then. Health insurance and Medicare are not affected by genetic test results. The genetic counsellor will explain the current rules and what they mean for you.
Have questions about familial bowel cancer syndromes?
Mr Nguyen sees patients at his consulting rooms in Heidelberg and operates at Warringal Private and Epworth Eastern. A GP or specialist referral is required.