Share on Pinterest
FatCamera/Getty Images

Colon cancer, also called colorectal cancer, is an umbrella term for cancer that starts anywhere in the colon or rectum. The American Cancer Society estimates that there will be 104,270 new cases of colon cancer this year.

Some cases of colon cancer will be MSI-high, or MSI-H, which stands for microsatellite instability-high. It refers to a piece of genetic coding and means there’s a lot of instability in the tumor.

Your MSI status gives your doctor an idea of how the cancer will behave. It can also help guide treatment decisions.

MSI-high colon cancer involves tumors with a high amount of instability. It occurs when mismatch repair (MMR) genes, whose job is to correct errors that happen during cell division, stop functioning properly.

When the MMR system is defective, it stops making repairs, allowing errors to accumulate. That’s how a tumor becomes highly unstable.

Doctors will use a tissue biopsy, usually following surgery, to test whether a tumor is MSI-high.

About 15 percent of colon cancer tumors are MSI-high, according to a 2016 study. About 3 percent of these are associated with a hereditary disorder called Lynch syndrome.

MSI-high cancer cells look and behave in an abnormal way. That’s not necessarily a bad thing when it comes to colon cancer, though.

While many cancer cells can easily hide from the immune system, MSI-high cancer cells stand out. That makes it easier for the immune system to recognize them as invaders. They also tend to respond well to treatment.

Treatment for colon cancer depends on several factors, such as the stage and location of the tumors. MSI status can play an important role in forming a treatment plan.

Here are some treatment options for colon cancer:


Surgery can remove many tumors in the colon.

In a procedure called segmental colectomy, the surgeon removes part of the colon, then attaches the ends together. In the early stages of colon cancer, surgery may be the only treatment you need.

Cancer that has spread to other organs or tissues can sometimes be surgically removed as well.


Regional and systemic chemotherapy can help shrink tumors and prevent cancer from spreading. It can be used alone or in combination with other treatments.

Chemotherapy drugs used to treat colon cancer include:

  • capecitabine (Xeloda)
  • fluoropyrimidine
  • irinotecan (Camptosar)
  • oxaliplatin (Eloxatin)


Immunotherapy is a promising treatment choice for many types of cancer. It’s a way of strengthening your own immune system to fight cancer.

Three immune checkpoint inhibitors are approved to treat MSI-high metastatic colon cancer. They’re all given through intravenous infusions.

Two of these drugs can only be used when cancer has progressed after treatment with certain chemotherapy drugs.

In 2017, the Food and Drug Administration (FDA) granted accelerated approval to nivolumab (Opdivo).

A year later, the agency granted accelerated approval to ipilimumab (Yervoy). This drug can only be used in combination with nivolumab, not by itself.

There’s also pembrolizumab (Keytruda). It’s a first-line immunotherapy for metastatic MSI-high colon cancer. That means you don’t have to try chemotherapy first. It was approved by the FDA in 2020.

In a clinical trial, researchers compared pembrolizumab to chemotherapy as a first-line therapy for MSI-high metastatic colon cancer. Pembrolizumab led to significantly longer progression-free survival. Trial participants who were treated with pembrolizumab also had fewer adverse events than those in the chemotherapy group.

Targeted therapy

Targeted therapies for colon cancer help prevent tumors from forming new blood vessels. These include:

  • bevacizumab (Avastin)
  • ramucirumab (Cyramza)
  • ziv-aflibercept (Zaltrap)

They’re administered intravenously, often in combination with chemotherapy.

Other drugs target epidermal growth factor receptor (EGFR), a protein that helps cancer grow. Some treatments include cetuximab (Erbitux) and panitumumab (Vectibix).

For cancer involving BRAF gene mutations, doctors may use targeted therapy drugs such as encorafenib (Braftovi) and regorafenib (Stivarga).


Radiation targets high-energy rays to a specific area of the body. This can help shrink tumors and kill cancer cells.

Treatment options for people with colon cancer have changed a lot in recent years, and there’s more to come.

Clinical trials help test innovative new therapies. Ask your doctor about clinical trials that may be a good fit for you.

According to the American Cancer Society, the 5-year relative survival rate for colon cancer is:

  • Localized: 91 percent
  • Regional spread: 72 percent
  • Distant spread: 14 percent
  • All stages combined: 63 percent

Keep in mind that these numbers are based on people diagnosed between 2010 and 2016. That’s before immunotherapies were approved to treat colon cancer. The outlook for people with the disease may be better today.

Outlook may be better in people with MSI-high colon cancer compared with MSI-low cancer. According to a 2018 study on 603 people who had surgery for colon cancer, those with MSI-high cancer had a slightly better survival rate.

While statistics can give you a sense of the outlook for people with colon cancer in general, your personal outlook can be different. It depends on a variety of factors, such as:

  • stage of cancer at diagnosis
  • genetic mutations
  • your age and overall health
  • choice of treatment and how well it works

Your doctor can review your health history to give you a better idea of what to expect.

MSI stands for microsatellite instability. MSI-high is a subset of colon cancer in which the tumor cells have a lot of instability. These cancer cells look and behave in an abnormal way.

The striking abnormalities make it hard for cancer cells to hide from the immune system. In general, MSI-high colon cancers respond better to treatment than other colon cancers.

Within the last few years, three immunotherapy drugs were approved to treat metastatic MSI-high colon cancers.

Two are for use when cancer hasn’t responded to chemotherapy.

The third, pembrolizumab, is now approved as a first-line treatment for metastatic MSI-high colon cancer.

Talk with your doctor to find out which MSI-high colon cancer treatment options are right for you.