Lynch Syndrome Detection and How Tumor Testing Can Identify Inherited Cancer Risk

A colon cancer diagnosis is hard enough. What many patients never hear is that the tumor itself can reveal whether the cancer runs in the family.

A lab test on tissue already removed during biopsy or surgery can point to an inherited condition called Lynch syndrome. That finding can change your treatment, your future screening, and the health of your siblings and children.

This testing doesn’t always happen, and when it does, the results aren’t always explained. This article covers how tumor testing works, what the results do and don’t mean, why it matters for families, and what to do in New York if an inherited risk was missed.

What Is Lynch Syndrome

Lynch syndrome is an inherited condition caused by a harmful variant in one of the genes that repair DNA copying errors: MLH1, MSH2, MSH6, or PMS2. A deletion in a nearby gene, EPCAM, can cause it by switching off MSH2.

Think of these genes as a proofreading team. Every time a cell divides, it copies its DNA, and small errors happen. Normally the mismatch repair genes catch and fix them.

In Lynch syndrome, the proofreading is weakened, so errors pile up, especially in short repeating stretches of DNA called microsatellites. Over time that buildup can lead to cancer.

Lynch syndrome is the most common inherited cause of colorectal cancer. CDC estimates that of roughly 400 Americans diagnosed with colorectal cancer each day, about 12 have Lynch syndrome, or about 3%. It accounts for a similar share of endometrial cancers.

It also raises the risk of cancers of the ovary, stomach, small bowel, pancreas, bile ducts, urinary tract, and brain. Our pages on colon and rectal cancer and endometrial cancer cover the basics of the two most common.

Each child of a carrier has a 50% chance of inheriting the variant, from either parent. Because it can pass quietly through a family without anyone connecting the dots, many carriers don’t know they have it.

How Tumor Testing Works

Tumor testing uses cancer tissue that was already collected, so nothing extra is required from the patient. The pathology lab runs one or both of two tests:

• Immunohistochemistry (IHC). Stains check whether the four mismatch repair proteins are present. If one or more is missing, the tumor is mismatch repair deficient (dMMR). If all four are present, it’s mismatch repair proficient (pMMR). Which proteins are missing hints at which gene is involved, since MLH1 and PMS2 travel as a pair, as do MSH2 and MSH6.

• Microsatellite instability (MSI) testing. This checks the repeating DNA stretches for the errors a broken repair system leaves behind. Many errors means MSI-high. Few or none means microsatellite stable (MSS).

The two tests agree most of the time, but not always. Broader tumor sequencing panels can also flag mismatch repair problems. When a panel finds a variant that might be inherited, guidelines encourage follow-up germline testing.

Confirming Lynch Syndrome With Genetic Testing

Confirmation comes from germline testing, which checks the DNA you were born with using a blood or saliva sample, usually as part of a multigene hereditary cancer panel. Results fall into three groups:

• Pathogenic or likely pathogenic. This confirms Lynch syndrome.

• Negative. No variant was found in the genes tested. A strong family history can still call for further evaluation.

• Variant of uncertain significance (VUS). Science doesn’t yet know whether the change matters. A VUS is neither a diagnosis nor a clean bill of health, and it can be reclassified later.

A genetic counselor can explain results, map your family history, and plan next steps. If you have an abnormal tumor result or a family pattern of cancer, asking for a referral is reasonable.

Who Should Be Tested

Guidance has moved from testing people who “look like” they have Lynch syndrome to testing everyone. A federal expert panel recommended back in 2009 that every person newly diagnosed with colorectal cancer be offered screening for Lynch syndrome.

Major organizations, including the National Comprehensive Cancer Network and the Society of Gynecologic Oncology, now support mismatch repair or MSI testing on all newly diagnosed colorectal and endometrial cancers, regardless of age.

The reason is that the older approach missed too many people. It relied on family history checklists such as the Amsterdam criteria and revised Bethesda guidelines.

Why Testing Changes Treatment

Mismatch repair-deficient and MSI-high tumors often respond well to immune checkpoint inhibitors, which help the immune system attack cancer cells.

On May 23, 2017, the FDA approved pembrolizumab for advanced MSI-high or dMMR solid tumors wherever they started. It was the agency’s first approval based on a tumor’s biology rather than its location.

Other immunotherapies have since been approved in specific dMMR settings, including dMMR endometrial cancer.

Some of the most striking work happened in New York. In a Memorial Sloan Kettering trial published in the New England Journal of Medicine, all 12 patients with dMMR rectal cancer who completed treatment with dostarlimab had a complete clinical response.

Their tumors could no longer be detected. The trial was small and the research is ongoing, but without mismatch repair testing, options like this may never be considered.

How Detection Protects Family Members

For many families, this is the biggest benefit. Once a variant is found in one person, blood relatives can be tested for that specific variant. This is called cascade testing.

Risk isn’t the same for every carrier. MLH1 and MSH2 carriers generally face the highest colorectal and endometrial risk. MSH6 and PMS2 carriers tend to face lower, later-onset risk.

Be wary of any source that gives one number for everyone. Our page on colon and rectal cancer screening protocols explains how average-risk screening differs.

Can You Sue If Lynch Syndrome Was Missed in New York?

Most people don’t ask this until something has gone wrong. A relative is diagnosed with advanced cancer and nobody ever mentioned genetic testing. Or an abnormal tumor result sat in a chart and was never acted on.

Whether there’s a claim depends heavily on the facts.

A New York malpractice claim requires showing that a provider departed from accepted standards of care and that the departure caused real harm.

Guidelines from groups like NCCN and the Society of Gynecologic Oncology are strong evidence of what a reasonable provider should do, though they aren’t automatically binding. Situations that can raise legal questions include a provider who:

• Never ordered mismatch repair or MSI testing when it was clearly indicated

• Didn’t follow up an abnormal tumor result

• Never referred the patient for genetic counseling or germline testing

• Never explained what the results meant

• Didn’t recommend appropriate surveillance after Lynch syndrome was confirmed

Causation and damages are usually the hardest parts. The key question is whether earlier knowledge would actually have changed what happened, for example by catching a later cancer sooner or preventing it.

These cases depend on expert testimony, and a complaint must be filed with a certificate of merit.

Timing needs particular care here. Under CPLR 214-a, the general malpractice deadline is two years and six months from the act or omission, or from the end of continuous treatment. For a negligent failure to diagnose cancer, Lavern’s Law instead runs the clock from when you knew or should have known of the error, with a seven-year outer limit.

Whether a doctor owes a legal duty to relatives who were never patients is also unsettled in New York. If you’re a family member asking about your own situation, bring that question to a lawyer.

Talk With a New York Cancer Lawyer

If you believe an inherited risk was overlooked, or an abnormal tumor result was never acted on, it’s worth having the records reviewed early, because these deadlines can run out quietly.

Our New York cancer lawyers work with oncology and genetics experts to review what was tested, what was reported, and what should have followed. You can also see our results in delayed cancer diagnosis cases.

Call 833-888-LATE, email info@porterlawteam.com, or request a free case evaluation.

Attorney advertising. This article provides general information and is not legal or medical advice. Laws, guidelines, and treatment approvals change. Prior results do not guarantee a similar outcome. Filing deadlines depend on the facts of each case.

Frequently Asked Questions

What is tumor testing for Lynch syndrome?

It’s a lab test on cancer tissue already removed during biopsy or surgery. Immunohistochemistry checks whether four DNA repair proteins are present, and microsatellite instability testing looks for the errors a broken repair system leaves behind. An abnormal result means the tumor is mismatch repair deficient or MSI-high, which can signal Lynch syndrome and calls for follow-up testing.

Does an abnormal MMR or MSI result mean I have Lynch syndrome?

No. Many mismatch repair-deficient tumors are sporadic, often because the MLH1 gene was switched off during life through methylation, especially in older patients. Labs check methylation and, in colorectal cancer, BRAF to sort this out. Lynch syndrome is confirmed only by germline genetic testing on blood or saliva, ideally with a genetic counselor’s help.

Should every colorectal and endometrial cancer be tested for Lynch syndrome?

Yes. Major organizations, including the National Comprehensive Cancer Network and the Society of Gynecologic Oncology, support mismatch repair or MSI testing on all newly diagnosed colorectal and endometrial cancers, regardless of age. Older family-history checklists missed too many carriers, so testing every tumor became the standard approach.

Can my family members be tested if I have Lynch syndrome?

Yes. Once your variant is identified, blood relatives can be tested for that specific variant, which is called cascade testing. Each child of a carrier has a 50% chance of inheriting it. Relatives who carry it can start early colonoscopy and other surveillance, while those who test negative can avoid unnecessary intensive screening.

Can I sue if my doctor never tested my tumor for Lynch syndrome in New York?

Possibly. A claim may arise if a provider failed to order indicated tumor testing, ignored an abnormal result, or never referred you for genetic counseling, and that failure led to a cancer being found later or not prevented. Causation is often the hardest part, and deadlines are fact-specific, so speak with a lawyer early.