Biomarker Testing

KRAS plays an important role in driving colorectal cancer cells to grow and divide. It is part of a pathway in tumor cells that can be triggered by activation of a receptor (think of an electrical socket) present on the surface of tumor cells. In this pathway, the receptor is known as the epidermal growth factor receptor (EGFR). If a biomarker test indicated a tumor has a KRAS mutation, then EGFR inhibitors (drugs that target EGFR) may NOT be beneficial because the receptor (think of the switch) on the cell wall, is permanently in the on position and cannot be turned off by available drugs. EGFR inhibitors include cetuximab (Erbitux) and panitumumab (Vectibix), and these are not generally used to treat people when their tumor is found to have a KRAS mutation.

KRAS testing is recommended for stage IV patients and at time of recurrence for any stage patient whose cancer recurs. There is currently no role for testing in stage I, II, or III CRC.

KRAS^G12C is a specific type of KRAS mutation, occurring in 3-4% of CRC patients. Current clinical trials are exploring KRAS^G12C targeted therapies in metastatic CRC.

KRAS wild-type means a tumor does not have a KRAS mutation. Patients whose test results show KRAS wild-type may respond well to certain treatment plans that include EGFR inhibitors.

KRAS testing is typically recommended for stage IV patients and stage III recurrence.

NRAS plays an important role in instructing colorectal cancer cells to grow and divide as part of the epidermal growth factor receptor (EGFR) process and has a similar function to KRAS. If a biomarker test indicates an NRAS mutation, EGFR inhibitors (drugs that target EGFR) may NOT be beneficial and may make the tumor grow faster. EGFR inhibitors include cetuximab (Erbitux) and panitumumab (Vectibix).

NRAS testing is recommended for stage IV patients and at time of recurrence for any stage patient whose cancer recurs. There is currently no role for testing in stage I, II, or III CRC.

NRAS wild-type means a tumor does not have an NRAS mutation. Patients who are NRAS wild-type may respond well to certain treatment plans that include EGFR inhibitors.

NRAS testing is typically recommended for stage IV patients and stage III recurrence.

BRAF is a gene that signals cells to divide. Approximately 1% of patients with mCRC have a tumor with a BRAF mutation other than BRAF V600E. The prognosis of the mCRC patients with tumors that harbor a BRAF mutation other than the specific V600e mutation is better than that of the average person with mCRC. Patients with a BRAF mutation may not respond to EGFR-inhibitor drugs, such as cetuximab (Erbitux) and panitumumab (Vectibix).

If a BRAF mutation is detected, there may be a poorer prognosis with the use of standard chemotherapy regimens; therefore, clinical trials may be a good option. Additionally, research is showing that emerging subgroups of the BRAF mutation can affect prognosis.

BRAF testing is typically recommended for stage IV patients. This test can be done at the same time as KRAS and NRAS testing. BRAF testing is also often done on stage II patients whose tumors are found to be MSI-H as a way to help determine if the MSI-H status of the tumor is inherited or acquired. There are specific drugs and drug combinations, which target BRAF mutations.

The presence of a BRAF V600e mutation suggests a particularly aggressive cancer that requires aggressive treatment. It is present in approximately 15% of patients with early-stage CRC and 6% of those with mCRC (mCRC).  Approximately 20% of patients with BRAF V600E–mutated mCRC also have MSI. Just like any other patients with MSI, these patients can respond to checkpoint inhibitors such as nivolumab and pembrolizumab. Additionally, vemurafenib is a drug that was included as a therapeutic option to treat BRAF V600e CRC in the 2018 version of the National Comprehensive Cancer Network’s Clinical Practice Guideline.

Current research is exploring combinations of immunotherapy and targeted therapy in patients with BRAF-mutated MSS CRC.

The PI3 kinase (PIK3CA) pathway contains genes needed for multiple cell functions including cell growth (proliferation) and survival. Testing for this mutation is not standard practice, per guidelines as of October 2017.

Patients with stage II or III (limited stage CRC) whose tumors harbor a PIK3CA mutation may benefit from aspirin therapy after surgical resection, as it can help decrease the risk of recurrent CRC.

Currently there are no recommendations for routine testing of PIK3CA, though testing may be suggested for stage I, II, and III patients. It is noteworthy that although PIK3CA inhibitor therapies have been approved for treatment of other types of cancer, this has not yet happened for colorectal cancer.

MSI-H, also referred to as “mismatch repair deficient” or “dMMR”, results when genes that regulate DNA (called Mismatch Repair Genes) don’t work correctly. Mismatch Repair Genes (MMR) work like genetic “spell checkers” by correcting errors that occur in the coding of DNA as cells divide. They work in a similar way to “spell checkers” that correct typos in a word processing program on a computer. When MMR genes stop functioning at their highest potential, areas of DNA could start to become unstable due to the errors leading to the development of a number of kinds of cancers including CRC.

An MSI screening test looks for changes in the DNA sequence between normal tissue and tumor tissue and can identify whether or not there is a high amount of instability. If this instability is present, those tumors are classified as MSI-High. Similarly, a dMMR test looks for the presence or absence of the mismatch repair proteins on special stains done on the tumor sample. In simple terms, MSI testing looks to see if the DNA is mutated and is not making the mismatch repair proteins (the “spell checkers”), and MMR staining looks to see if the MMR proteins are actually present in white blood cells that are present in blood. Both tests achieve the same result to determine whether the tumor is MSI-H, also called dMMR.

MSI-H or dMMR is found in about 15% of colon tumors. About a quarter of MSI-H or dMMR tumors are associated with the hereditary syndrome, Lynch syndrome, though many MSI-High tumors are sporadic (not due to a hereditary syndrome).

While 15% of all CRC tumors are MSI-high or dMMR, only about 4% of patients with mCRC will have MSI or dMMR tumors. Those who do have MSI-H or dMMR metastatic tumors are the small subset of patients who are likely to benefit from treatment with currently available immune checkpoint inhibitors.

MSI or MMR testing is recommended for ALL colorectal cancer patients. Talk to your surgeon or oncologist about MSI or MMR testing.

CEA (or Carcinoembryonic Antigen) is a protein that is commonly elevated in CRC patients and is present in low levels in healthy people or modestly elevated levels in individuals with inflammation of the colon. In patients with mCRC, higher levels of CEA may indicate that cancer is growing while lower levels may indicate that treatment is working. Not all patients with CRC will have an elevated CEA.

Research suggests there may be a difference in biology, depending on the side of the colon that cancer originates (right versus left). Based on the research, patients with right-sided tumors may not have the same results and success rates if EGFR-inhibitor therapy is used as the first line of treatment as compared to patients with left-sided tumors. In those patients the targeted agent bevacizumab is often recommended in addition to standard chemotherapy.

HER2 (or human epidermal growth factor receptor 2) is being studied as a possible pathway that can be targeted with available drugs, which can be overactive in patients with KRAS wild-type tumors. In approximately 5% of KRAS non-mutated (wild-type) cancers, HER2 is amplified. Combination therapies including trastuzumab and lapatinib have been tested with these patients in phase II studies, resulting in a 35% overall response rate and a median time to progression of about five and a half months.

Tropomyosin Receptor Kinase (TRK) fusions are genetic abnormalities that occur when one of the NTRK genes (NTRK1, NTRK2, NTRK3) become connected (fused) to another gene that is not related (e.g., ETV6, LMNA, TPM3). This connection leads to TRK signaling that is uncontrolled and could lead to cancer. TRK fusions are rare; however, when they are present, there could be an option for a clinical trial for treatments targeting TRK inhibition. Additionally, new drugs, which target NTRK fusion-positive mCRC have recently been approved, including entrectinib and larotrectinib. These have been approved for metastatic solid tumors that have either progressed following prior therapies or as initial therapy when there are no acceptable standard therapies.

PD-L1 is an immunosuppressive driver, meaning that it stops the immune system from functioning at its optimal level. Some cells within the body, called T-cells, have receptors on them which make sure that abnormal or mutated cells don’t multiply.

Think of these T-cells as security guards and PD-L1 as a disguise on abnormal cells. With the presence of PD-L1, the T-cell receptors are unable to see that the mutated cells are mutated due to the PD-L1 “disguise”; therefore, the mutated cells get through the security guards and are able to multiply, becoming cancer. Nearly half of all cancers have the PD-L1 biomarker. Therefore, many researchers are using the presence of PD-L1 as a pathway to fight cancer.

TMB is a biomarker made up of the total number of mutations per coding area of a tumor genome. Some researchers are now using it to identify which patients would benefit from the checkpoint inhibitor therapy (like ones that target PD-1/PD-L1). A high level of TMB may indicate that you would benefit from this type of treatment.

The Wnt pathway is a complex pathway responsible for stability and is often highly mutated in colorectal cancer patients. When not functioning properly, the pathway could lead to mutations in adenomatous polyposis coli (APC) genes in the body, which are found in most of all sporadic colorectal cancer in addition to familial adenomatous polyposis (FAP — a heritable syndrome. To learn more, download our Genetics Mini Magazine). Targeting the Wnt pathway, especially through the use of combination therapies, is something researchers are studying for more effective treatment plans.

Currently, only MSI testing is recommended. However, it is strongly recommended that all CRC patients learn about their family health history of colon and rectal cancers. Depending on the history, patients will be referred to genetic counseling to learn if they are at a higher risk for developing other cancers or if their family members are also at a higher risk.

Talk with your healthcare team about tumor biomarker tests immediately after your diagnosis. If you are already on treatment and are unsure whether or not you have received biomarker testing, ask your treatment team.

Your test results will show whether your tumor has a mutation (positive test results) or if it is wild-type (negative test results; no mutation detected). Your doctor will review your test results with you and discuss how they will affect your treatment decisions. If you would like a copy of your test results, be sure to request them. Finally, if you have questions for your treatment team, be sure to ask!

It would be extremely rare. If you have a BRAF-mutant tumor, you most likely will not be KRAS mutant, and vice versa.

No. When you had surgery, some of your tumor tissue was removed and stored at the hospital. Your doctor can arrange for your tissue to be sent to a lab. Results will go to your doctor. The tissue sample tested can be from your original cancer in your colon or rectum, or from a metastatic tumor that has spread.

Your provider should be discussing biomarker testing with you. If they haven’t, be sure to advocate for your care and start the discussion. Our biomarker testing discussion guide is a great place to start.

There are multiple biomarkers that have been scientifically shown to be meaningful in colorectal cancer. While more and more biomarkers are being studied, not all are shown to have clinical relevance or benefit the patient’s treatment decision-making.

Genetic testing is a type of biomarker testing, but does not ensure that you have received all the biomarker tests necessary to make an informed treatment decision.

This means that you have received MSI testing. To learn if you have received testing for additional biomarkers, you will need to check with your doctor.

Your doctor will likely explain the results of your biomarker test with you when they come in. If they don’t, just ask! Additionally, if you’d like to keep a copy of the report for your records, don’t hesitate to ask for one. Make sure you clearly understand the results, so that you can participate in shared decision-making for your treatment plan.

If you are participating in a clinical trial, the trial may cover the cost of biomarker testing. Private individual or employer-sponsored health insurers will usually cover biomarker tests when they are “medically necessary.”

Some people may avoid testing due to perceived financial burden. Luckily, many labs offer patient assistance for out-of-pocket costs, and insurance companies may cover costs as well. Talk to your social worker and call your insurance provider to learn more.

In May 2017, four professional groups published evidence-based guidelines for biomarker testing for colorectal cancer. The Guideline, titled Molecular Biomarkers for the Evaluation of Colorectal Cancer Guideline from the American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology, and American Society of Clinical Oncology provides recommendations for mismatch repair status testing. RAS mutation testing for patients being considered for anti-EGFR therapy, and BRAF testing for colorectal cancer patients, in addition to other recommendations and expert consensus opinions for the implementation of biomarker testing. As research continues to evolve, guidelines and recommendations will also likely change to reflect the most relevant and meaningful research.