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Last month, we updated you when the FDA gave pembrolizumab (Keytruda) breakthrough status, which will speed up the development and review for the drug’s FDA approval. Now, stage IV survivor and Colon Cancer Alliance Medical Advisor and Patient Advocate Dr. Laura Porter gives us more insight into why this new drug and its breakthrough status is an important step forward. 

The FDA has just given pembrolizumab (Keytruda) breakthrough status. Can you explain why this is so important to the colon cancer community?

Preliminary data presented at the American Society of Clinical Oncology’s (ASCO) Annual Meeting was incredibly exciting. This is the first drug of its kind to work in colon cancer (it is already FDA approved for use in melanoma and some lung cancers). It is monoclonal antibody, which uses a patient’s own cells to kill cancer by enabling the body’s natural immune response to tumor cells. The catch is, however, this drug is only effective for a small group of patients:

  • Those who have Lynch Syndrome
  • Those who are MSI-H (MSI-high)

As you mentioned, this is particularly great news for the small percentage of those with MSI-H. What does it mean to have MSI-H?

MSI stands for microsatellite instability.

If you remember from high school biology class, the human body has hundreds of thousands of cells that are dividing and multiplying at any given time. Each time a cell divides, its DNA is copied from the old cell to the new cell. Normally, the DNA in the new cell is identical to the DNA in the old cell, but occasionally, the cell doesn’t quite get the copy correct and a small section of the DNA (also known as a microsatellite) has a small error and doesn’t quite match the original.

In any person, these errors are normal and the human body is designed with a built-in mechanism to naturally fix these mismatches. However, if you are MSI-high, your body has a deficiency in the mismatch repair mechanism. This is found in about 15-20 percent of all colon cancers, including those with Lynch Syndrome.

In the case of pembrolizumab, being MSI-high is great news, as it means you will be a great candidate for the drug.

In addition to the FDA breakthrough status, Merck is also planning to launch a phase III trial for pembrolizumab. What advice do you have for patients interested in entering this, or other, clinical trials?

First we have to dispel the myth that you’re going to be a “guinea pig” when you enter a clinical trial. Clinical trial participants are not guinea pigs; they are the first people to receive a drug that’s already been tested and showing promise—particularly in phase II and phase III trials. Clinical trials are designed to give all enrollees access to the drug if it shows early promise, therefore reducing the wait time for it to get approved and on the market. 

I would also suggest getting as much information as you can; visit the Colon Cancer Alliance website for useful information about clinical trials and speak with your doctor if you’re interested in entering one. The Colon Cancer Alliance also has a Clinical Trial Matching Service where a patient navigator can help you learn which clinical trials are right for you. 

Want more information on the latest treatment and research updates? The Colon Cancer Alliance serves as a source of information about colon health. If you have additional questions about colon cancer treatment or are in need of support, please contact our free Helpline at (877) 422-2030. We’re here to help.


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