Genetic Testing for Colorectal Cancer: When Is It Recommended? (2026 Update)

Testing to determine whether a colorectal cancer has a hereditary basis is generally recommended when there is a family history or when the cancer is diagnosed at a young age. Because the results can affect when family members should start screening and how often they should be screened, it helps to organize your family history in advance.

Key Takeaways

• Testing for hereditary colorectal cancer is sometimes recommended when there is a family history or when the patient was diagnosed at a young age.
• Depending on the results, not only the patient but also family members may need to adjust the age at which they start screening and how often they are screened.
• For advanced or metastatic colorectal cancer, marker tests such as MSI/MMR, RAS, BRAF, and HER2 are performed separately to guide drug selection.
• Korea's 5-year relative survival rate for colorectal cancer is 75.6% (National Cancer Registry Statistics, 2019–2023); this is a nationwide figure, not the outcome of any single hospital.
• International patients can bring their treatment history, tissue slides or paraffin blocks, and existing genetic test results so that review and additional testing can be arranged in Korea.

Why Is Hereditary Colorectal Cancer Testing Recommended, and for Whom?

• Colorectal cancer is a well-characterized cancer in which polyps gradually grow over time and become malignant, and some cases are linked to a hereditary predisposition. Testing to check for hereditary colorectal cancer is generally recommended when there is a family history or when the cancer is diagnosed at a young age.
• This testing matters because it affects not only the individual patient's treatment plan but also future screening plans for family members. Since the results can change the age at which relatives should begin screening and how frequently they should be screened, it is helpful to compile information beforehand on whether multiple family members have had the same type of cancer, before your consultation.
• Separate from testing for hereditary status, advanced or metastatic colorectal cancer requires its own set of marker tests (MSI/MMR, RAS, BRAF, HER2) to select the appropriate treatment drugs. Cases confirmed as MSI-High are known to respond particularly well to immunotherapy, making this result a key piece of information that can determine the direction of treatment.

What Is the Sequence of Testing and Result Review?

• Step 1 — A colonoscopy is performed to check the location and size of the lesion, along with a biopsy.
• Step 2 — Abdominal and chest CT (plus pelvic MRI for rectal cancer) is used to assess metastasis and lymph node status.
• Step 3 — CEA tumor marker levels are measured in the blood, and PET-CT may be selectively performed if metastasis is suspected.
• Step 4 — For advanced or metastatic colorectal cancer, additional marker tests (MSI/MMR, RAS, BRAF, HER2) are performed to serve as the basis for drug selection.
• Step 5 — For patients with a family history or those diagnosed at a young age, separate testing for hereditary colorectal cancer is recommended, and the results are shared with family members to adjust their screening plans.

FAQ — Can Genetic Test Results from Another Country Be Used As-Is?

In most cases, yes, they can be used as reference. However, because testing methods and standards vary between institutions, markers that are critical for drug selection are sometimes re-confirmed in Korea using paraffin tissue blocks. Bringing slides or paraffin blocks with you allows for review and additional testing to be arranged.

FAQ — Should Family Members Also Get Tested?

Testing for hereditary colorectal cancer is recommended when the patient was diagnosed at a young age or when multiple family members have had the same type of cancer. Since the results can affect the age at which family members should start screening and how often they are screened, organizing your family history in advance is helpful for the consultation. Whether testing is needed and how extensive it should be is decided individually based on each person's situation.

Sources and Notes

• This article was written based on the Colorectal Cancer Notes (National Cancer Registry Statistics 2019–2023, Central Cancer Registry, National Cancer Center Korea), the NCCN Guidelines for Patients, and SEER.
• This content is intended for general medical information purposes only. Diagnosis, treatment methods, and outcomes may vary depending on individual circumstances. Accurate diagnosis and treatment should always be determined through consultation with a medical professional.