What is ROS1-positive lung cancer?

If you or a loved one is living with cancer and making treatment decisions, an important concept to understand is “biomarkers.”

Biomarkers or “biological molecules” include things like specific proteins or gene mutations that provide information about how a cancer is or is not behaving. Biomarker testing is performed by taking a sample of a tumor, tissue, or fluid (like blood) and sending it to a specialized lab for analysis.

Biomarkers have played a critical role in cancer treatment over the past decades, allowing healthcare providers to predict what drugs a cancer is more likely to respond to and enabling the development of drugs that target specific cancer biomarkers.

ROS1 is a biomarker found in a small subset of non-small cell lung cancers (NSCLCs). Here are three things to know.

It involves a type of mutation called gene fusion

Genes are segments of DNA that contain instructions for making specific proteins. The ROS1 gene contains instructions for making ROS1, a protein that helps guide the growth and development of cells. Normally, a protein like this will be active at times and inactive at others, a tightly regulated process that protects against the formation of tumors.

In certain cases of NSCLC (and other cancers), the ROS1 gene has undergone a mutation called fusion or rearrangement, where it has broken open and merged with another gene. This creates a ROS1 protein that is overly active and drives uncontrolled cell growth.

Lung cancers that test positive for this mutation are said to be ROS1-positive.

ROS1 mutations are rare

Less than 2 percent of NSCLCs are ROS1-positive. These mutations are not related to smoking (the leading cause of lung cancers) and can be found in people with no history of smoking or minimal history of smoking as well as smokers

To test for a ROS1 fusion, a healthcare provider will perform a biopsy, collecting a tissue sample from the tumor that will be tested in a lab. Biopsies are a standard diagnostic test for lung cancer and check for numerous biomarkers and cancer cell characteristics.

Liquid biopsy, which involves collecting and testing a blood sample, may also be used in certain cases.

There are therapies that target ROS1

Biomarkers are also potential targets for cancer treatments. If a specific mutation or protein is driving cancer growth, blocking or shutting down that biomarker can potentially shrink tumors or slow the growth of cancer. Drugs that work like this are called targeted therapies and have become an essential part of cancer treatment in recent decades, including the treatment of NSCLCs.

There are targeted therapies for ROS1-positive NSCLC, called ROS1 tyrosine kinase inhibitors (TKIs) or ROS1 inhibitors. These drugs work by blocking the abnormal, overactive ROS1 protein produced by genes that have undergone ROS1 fusion.

It’s also important to mention that ROS1-positive lung cancer can develop resistance to these treatments over time. If this occurs, your healthcare team will recommend the next steps. This may involve switching medications and/or repeating biopsy and biomarker testing to determine what other treatments might be effective. Clinical trials may also be an option.

Also, research is ongoing. Treating ROS1-positive NSCLC that has become resistant to treatment is a focus of research.

Keep in mind that the information above is a simplified explanation of complex cellular processes and drug mechanisms, intended to help prepare you for conversations with your healthcare team, who will be your best source of information.

Before starting any cancer therapy, it is important to understand what the therapy is, how it works, why it is recommended, and the potential side effects.