I am 34, male with NSCLC. What is the role of MSI testing?

Question

Hello doctor,

I’m 34 years old and weigh 149 lbs. I have recently been diagnosed with non-small cell lung cancer and my doctor said that I will have several tests before I can start immunotherapy. I’ve heard of PD-L1 testing, genetic mutation testing, and MSI testing, but I don’t really get what they are.What is the role of MSI testing in non-small cell lung cancer? I am 34 years old. Does it matter for treatment decision-making?

Please advise.

Thank you.

Answer 1

Hello,

Welcome to icliniq.com.

Thank you so much for sharing your concern with me.

It’s understandable to be confused when you’re given a diagnosis of non-small cell lung cancer and several different tests are mentioned. Usually, before treatments such as immunotherapy can begin, doctors will perform a number of molecular tests on the tumor tissue. These tests provide us with information about the biological behavior of the cancer and guide the choice of treatment that is most suitable for each patient.

Testing for PD-L1 (programmed death-ligand 1) is one of the main tests before immunotherapy. This test examines the amount of a specific protein on the surface of the cancer cells. The finding is often useful for doctors to decide whether to include immunotherapy in the treatment plan, as sometimes immunotherapy drugs are more effective when PD-L1 levels are higher.

Genetic mutation testing is also very important, especially in younger patients with lung cancer. The test looks for certain gene changes such as EGFR (estimated glomerular filtration rate), ALK (anaplastic lymphoma kinase), ROS1 (ROS proto-oncogene 1, receptor tyrosine kinase) and others. If you have one of these mutations, your doctor may try targeted therapy. These treatments are made to work on those specific mutations and can be very effective.

MSI testing = microsatellite instability testing. It looks for a defect in the DNA (deoxyribonucleic acid) repair system of the cancer cells. In some types of tumours, this repair system is not working well, and these can then accumulate many genetic changes and sometimes respond well to immunotherapy.

However, MSI-high tumours are relatively uncommon in lung cancer compared with some other cancers, such as colorectal cancer. As a result, MSI testing is generally not the main factor in treatment selection for most patients with lung cancer, although it can be included as part of a broader molecular assessment.

In practice, the most influential results for treatment decision-making in non-small cell lung cancer are typically the genetic mutation panel and the PD-L1 level. MSI testing provides more information but is generally less influential in treatment decisions.

I hope this helps you.

Thank you.