Australia's Definitive Guide to the Lynch Syndrome

Lynch syndrome is one of the most common and underdiagnosed inherited cancer conditions in Australia. It is a hereditary condition that significantly increases your lifetime risk of developing cancer, especially endometrial cancer and colorectal cancer. For many Australians, a diagnosis of Lynch syndrome (non-polyposis colorectal cancer) is a turning point, enabling a transition into a well-defined proactive plan for a healthy life.

Here is an overview of Lynch syndrome with 15 things you need to know about this hereditary cancer:

1. The Biology: What is a "Mismatch Repair" Gene?

To understand Lynch syndrome, you first have to understand how your body grows. Your body is made up of trillions of cells, and every one of those cells needs to divide over and over again to create all the new cells that your body needs. When a cell divides, it makes a copy of all its DNA. The instructions in your DNA stretch for around 3 billion letters.

Whenever a cell copies its DNA, some mistakes are going to happen. Most of the time, people have a set of genes called Mismatch Repair (MMR) genes. Mismatch repair genes work like an advanced spell-checker. They look at the new copy of your DNA and search for mistakes.

They fix most of those mistakes. In people with Lynch syndrome, one of their biological spell-checkers (MLH1, MSH2, MSH6, PMS2, or EPCAM) has an error from birth. This genetic mutation means that, over time, mistakes that cannot be corrected accumulate in certain cells, leading to uncontrolled tumours.

2. An Underdiagnosed Condition in Australia

Around 1 in 280 Australians carries a Lynch syndrome gene mutation, but only about 5% are diagnosed. That’s why it’s called an invisible condition.

Traditionally, you would not be diagnosed with Lynch syndrome until multiple common cancers had occurred in your family members. Common cancers linked to Lynch syndrome include colorectal cancer, endometrial cancer, ovarian cancer, and urinary tract cancers.

Now, thanks to better commonly reported pathology and universal screening in Australian hospitals, we are much better at identifying potential Lynch syndrome carriers before they get diagnosed with cancer at all.

3. The 50/50 Chance: Understanding Inheritance

Lynch syndrome is an autosomal dominant condition. This means it does not skip generations; it is inherited from the parents and is not linked to your biological sex.

• If one of your parents has the syndrome, you have a 50% chance to inherit Lynch syndrome.
• If you do not have the condition, you cannot pass it on to your children.
• Your siblings have a 50% chance of being affected too.

This high probability of inheritance is why communication with other family members is so critical. Often, one person’s cancer diagnosis is the key that unlocks a life-saving door for their entire extended family.

4. The Most Common Risk: Bowel (Colorectal) Cancer

For both men and women, the most significant Lynch syndrome-associated risk is bowel cancer. For the general population, the lifetime risk to develop colorectal cancer is around 5%.

The lifetime risk of developing colorectal cancer for Lynch syndrome carriers is significantly higher than for the general population, estimated between 40% and 80%.

Another important thing to note is that Lynch syndrome bowel cancers occur at a much younger age, in the 30s and 40s, than sporadic (non-genetic) bowel cancers.

They also grow much more aggressively than sporadic bowel cancers.

This is why simple stool testing to check for blood in the stool is not enough for someone at increased risk of Lynch syndrome-related cancers.

Also, general guidelines for getting a colonoscopy at age 50 are not appropriate. These Lynch syndrome patients require extensive monitoring.

5. The "Sentinel" Cancer: Uterine (Endometrial) Cancer

Women are as likely to get uterine and ovarian cancer as they are to get bowel cancer.

In the female reproductive system, it is often the sentinel cancer that appears first. It is not uncommon for a woman to be diagnosed with Lynch syndrome only after uterine cancer appears in her late thirties.

Women with Lynch syndrome have a 40% to 60% chance of developing endometrial cancer. Detecting it in time allows you to take measures to reduce cancer risk that protect the bowel and ovaries.

Women with Lynch syndrome may be advised to have a hysterectomy and oophorectomy to prevent endometrial and ovarian cancer.

6. The "3-2-1" Rule for Families

If you are looking at your family cancer history and are not sure if you could have the genetic condition, doctors use clinical criteria like the Amsterdam Criteria II to determine if you should be screened for Lynch syndrome. You should use this molecular genetic testing if your family has:

• 3 relatives with a Lynch syndrome-associated cancer (bowel, uterine, small bowel, ureter, or renal pelvis).
• 2 successive generations (relatives) affected.
• 1 generation (relatives) diagnosed before age 50.

Even if you don’t meet these criteria, "de novo" mutations (new mutations that start with you) can occur, so clinical suspicion and reviewing strong family history are important.

7. Universal Screening: Australia’s Safety Net

Australia is a world leader in Universal Screening for hereditary non-polyposis colorectal cancer.

All major hospitals now routinely do Immunohistochemistry (IHC) on all removed bowel and uterine tumours during surgery. It looks for the four spell-checker proteins. If they are absent, it alerts the doctors that the patient likely has Lynch syndrome.

This is a framework designed to prompt a referral for genetic counselling, even in the absence of family history.

8. The Path to Diagnosis: Blood vs. Tumour

There are two routes to genetic testing:

• The Tumour Test: Looks only at the tumour. It tells you whether the spell-checkers were working on that tumour.
• The Germ-line Test: A blood test that tells you if you were born with the gene mutation or if it only exists in the cancer cells. In Australia, these tests are largely Medicare reimbursed if you meet the criteria, allowing for a confirmed diagnosis.

9. Cascade Testing and the "Family Letter"

Once you have identified a genetic mutation in a family (the index case), cascade or predictive testing begins. Your genetic counsellor will have a "Family Letter" for you. It is a powerful tool. It tells your relatives exactly what gene mutation has been identified in your family. It gives them a road map. This allows your siblings, children, and cousins to have their targeted blood tests for hereditary cancer syndromes.

10. The Power of the 1–2 Year Colonoscopy

For the average individual, a colonoscopy may be required every ten years or so. For a person with Lynch syndrome, it is normally required every 1 to 2 years.

That's because a colonoscopy is the most recommended screening test for individuals with Lynch syndrome to detect changes in the bowel. Routine high-quality colonoscopies are recommended every 1 to 2 years, often starting in the early-to-mid 20s for individuals with Lynch syndrome.

Why so often? Because in Lynch syndrome, polyps turn malignant much more rapidly than they do in the general population. By going for a colonoscopy every 12 to 24 months to treat cancer early, polyps can be snipped out before they become malignant, significantly lowering your cancer risk.

11. Aspirin: The Australian Breakthrough

One of the most exciting findings of the CAPP2 and CAPP3 studies (with heavy Australian involvement) was that taking daily low-dose aspirin may reduce the long-term risk of colorectal cancer in Lynch syndrome carriers by roughly 50%.

Clinical guidelines now frequently advise aspirin chemoprevention from the commencement of colonoscopic surveillance. Because aspirin carries risks such as gastric irritation or bleeding, it is essential to discuss the appropriate dose and suitability with your GP or specialist.

12. Preventative Surgery (Prophylactic Options)

The uterine and ovarian cancer risks for women can be managed with surgery. Most women choose to undergo a prophylactic hysterectomy and oophorectomy once they are done with childbearing (usually around age 40) to manage their risks early.

This removes the target organs and is very liberating. Furthermore, surgery remains the front-line therapy for Lynch syndrome, particularly for colorectal cancer.

13. Extra-Colonic Risks

Lynch syndrome can also affect the stomach, urinary tract, pancreas, and other organs. There is no simple test for these extra-colonic risks, but your specialist may recommend:

• Gastroscopy: To check the stomach lining for gastric cancer.
• Urinalysis: To look for blood in the urine, which could signal a kidney or ureter problem.
• Dermatology tests: To monitor rare skin cancer tumours.

14. Genetic Testing and Insurance in Australia

One major worry for many Australians is insurance discrimination.

• Private Health Insurance: The Australian Private Health Care Ombudsman says that you can’t be denied cover or have your premiums loaded for private health insurance based on a genetic test.
• Life and Income Protection Insurance: The Australian Financial Services Council has a moratorium, so you do not usually have to disclose a favourable or unfavourable test result when applying for life or income protection insurance for policies up to a limit. As of today, that limit is $500,000. Always check with your genetic counsellor when applying.

15. Reproductive Options (IVF and PGT)

For young Australians, the “50/50” inheritance problem can feel intense when considering starting a family. Thankfully, modern medicine offers interventions such as Pre-implantation Genetic Testing (PGT).

If a couple undergoes IVF, they can test embryos for the Lynch syndrome gene mutation and implant only unaffected embryos. So you can stop the cycle of early cancers for the next generation of your family.

Conclusion: Knowledge is the Best Medicine

Lynch syndrome has no symptoms until the cancer develops. The difference is whether you catch it early. With testing, surveillance, and proactive management, you can significantly reduce and manage your risk profile. The Everlab program champions this proactive approach through its genetic, imaging, and longitudinal testing.

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Sources

1. ‍DNA, RNA, genes and genomics- Institute of Molecular Bioscience, University of Queensland
2. ‍Lynch syndrome- Cancer Australia
3. ‍Lynch Syndrome: Genetic Testing and Management- Our Cancer Stories, National University of Singapore Initiative
4. ‍Genetics and Lynch Syndrome-University of California, San Francisco
5. ‍Diagnostic & Tumor testing criteria- Lynch Syndrome Screening Network