KRAS Testing for Colorectal Cancer

Is Testing Right for Me? I Have My Test Results

KRAS Testing for Colorectal Cancer

How KRAS Testing for Colon Cancer Works

There are several different ways to test for KRAS gene mutations. Each test uses different technology and has its own pros and cons.

In colon cancer tumors, there are seven common mutations in the KRAS gene. All KRAS tests should look for at least these common mutations. Testing for these seven mutations will find up to 95% of all advanced colon cancer KRAS mutations. Some tests look for more mutations.

Common KRAS Mutations

34G>C (G12R)    35G>C (G12C)    34G>A (G12S)    35G>A (G12D)
35G>C (G12A)    35G>T (G12V)    38G>A (G13D)

If you test negative for the seven most common KRAS mutations, your chance of having a KRAS mutation that isn't found by the test is low (about 5%), but it isn't zero. It is possible to have an uncommon mutation.

Testing Types

In general, there are two kinds of KRAS testing.

  1. Mutation testing that looks for a group of specific mutations, like the seven listed above. It is cheaper than looking at the whole gene for mutations and is very efficient. It can work with small amounts of tumor tissue and is very reliable. However, it can only find what it is looking for, and it looks for common mutations. It will miss the uncommon mutations that happen in about 5% of colon cancer tumors. Medical guidelines recommend testing for at least the seven most common KRAS mutations.
  2. Gene sequencing looks at the whole gene for any mutations, not just for specific mutations. It requires more tumor tissue, is more labor-intensive, and is generally more expensive than looking for specific mutations. However, it can find both common and uncommon mutations.
Next: Pros and Cons

Do you have advanced colorectal cancer?

Yes

No

Are you considering or are you on anti-EGFR therapy (such as Erbitux® or Vectibix®)?

Yes

No

KRAS gene testing is not likely to be useful for you.

Current medical guidelines from the American Society of Clinical Oncology (ASCO) and the National Comprehensive Cancer Network (NCCN) recommend KRAS gene testing for people with advanced colorectal cancer who are considering anti-EGFR therapy. Although other tumor types have KRAS mutations, KRAS gene testing is only recommended for colorectal cancer.

KRAS gene testing may be useful for you.

Current medical guidelines from the American Society of Clinical Oncology (ASCO) and the National Comprehensive Cancer Network (NCCN) recommend that genetic testing for KRAS mutations should be done for all patients considering or who have recently begun EGFR-targeted therapy with Erbitux® (cetuximab) or Vectibix® (panitumumab) who have advanced colorectal cancer.

KRAS testing can help predict if you will respond to a treatment for colon cancer called EGFR-targeted therapy (Erbitux® or Vectibix®). Patients with a KRAS mutation in their tumor should avoid treatment with these drugs.

The table below sums up how test results can change your care.

Possible Test Results and What They Mean

Test Result Category Chance To Get This Result What This Result Means
KRAS mutation positive About 40%
  • Your colon cancer is not likely to respond to EGFR-targeted therapy.
  • Anti-EGFR therapy may make your condition worse.
  • Medical guidelines recommend avoiding treatment with Erbitux® or Vectibix®.
  • Other kinds of therapy may work better for your tumor.
KRAS mutation negative About 60%
  • Your colon cancer has a good chance of responding to EGFR-targeted therapy.
  • Depending on your situation, EGFR-targeted therapy may be used alone or combined with chemotherapy.
  • If your tumor didn't respond to earlier chemotherapy, or if chemotherapy has stopped working, you may benefit from the addition of EGFR-targeted therapy.

KRAS gene testing may not be useful for you, because you don't have advanced colorectal cancer. Advanced colorectal cancer is the only cancer for which KRAS gene testing is recommended before starting anti-EGFR therapy.

Erbitux®, an anti-EGFR therapy, is also approved for the treatment of certain head and neck cancers. However, current medical guidelines do not recommend KRAS gene testing before starting Erbitux® for these types of cancers.

Current medical guidelines from the American Society of Clinical Oncology (ASCO) and the National Comprehensive Cancer Network (NCCN) recommend KRAS gene testing for people with advanced colorectal cancer who are considering anti-EGFR therapy. Research is being done to find out whether KRAS gene testing might be helpful for other tumor types, but at this time it is not recommended for other cancer types.

KRAS gene testing may not provide information useful to you because you are not considering anti-EGFR therapy.

Current medical guidelines from the American Society of Clinical Oncology (ASCO) and the National Comprehensive Cancer Network (NCCN) recommend KRAS gene testing before starting treatment for all patients with advanced colorectal cancer. However, KRAS gene testing is mostly useful for deciding whether anti-EGFR therapy (Erbitux® or Vectibix®) is appropriate treatment. If anti-EGFR therapy is not being considered for treatment of your cancer, KRAS gene testing probably won't provide you useful information.