Blood Test Could Predict the Best Type of Treatment for Metastatic Melanoma

Checkpoint inhibitors, such as ipilimumab (Yervoy), nivolumab (Opdivo), and pembrolizumab (Keytruda), help the immune system recognize, attack and kill cancer cells. Targeted drugs, such as dabrafenib (Tafinlar) and trametinib (Mekinist), disable the gene in the tumor that helps it grow.

Dr. Anna Pavlick explains how targeted therapy works in melanoma.

Doctors don't yet know how to determine who will respond to checkpoint inhibitors and who would do better starting out on targeted therapy. Which one to try first remains a topic of debate. But new research suggests that, for those who haven't yet started therapy, a liquid biopsy — a type of blood test that looks for pieces of tumor DNA that may be circulating in the blood (ctDNA) — might help take the guesswork out of treatment decisions for people with metastatic melanoma.

"Liquid biopsy is an exciting field with lots of potential applications and a lot of promise," Marko Spasic, MD, medical director of the Parker Institute for Cancer Immunotherapy, tells SurvivorNet.

Predicting Response to Immune Checkpoint Inhibitors

In this new study, researchers looked at the levels of tumor DNA circulating in the bloodstreams of people with metastatic melanoma before they received their first treatment. They also measured ctDNA levels in a group of people before they started their second treatment after their cancer had progressed on a first-line treatment.

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What they found was that people who had the lowest levels of ctDNA to begin with tended to have the longest progression-free survival and overall survival on first-line immune checkpoint inhibitors. Higher levels of ctDNA were associated with poorer response to first-line immune checkpoint inhibitors. CtDNA levels didn't help predict how patients would respond to checkpoint inhibitors as a second-line treatment. The study findings suggest that liquid biopsy may soon aid doctors in treatment decisions for people with metastatic melanoma who have not yet begun their care.

Liquid Biopsy Detects Tumor DNA in the Bloodstream

A liquid biopsy is a blood test that can detect cancer cells or bits of DNA from a tumor in your bloodstream. This type of test could be part of your screening for the presence of cancer; aid in decisions about your treatment; help monitor your response to treatment; or detect remaining cancer in your body or a recurrence.

Related: FDA Approves Blood Test that May Help Some Patients Avoid Additional Biopsies

"The use of liquid biopsy is being rolled out across many different phases and types of cancer treatment," Spasic says.

This blood test is a less invasive way to monitor cancers and treatment responses compared to tissue biopsies. But, for now, tissue biopsy will remain the gold standard. Researchers don't yet know to what extent they can rely on information collected from a liquid biopsy to replace the results of a tissue biopsy.

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"It's another data point, one more of multiple data points, that can help refine an assessment. Doctors are putting it into practice in melanoma and other tumor types," Spasic says.

With more research, doctors could one day use liquid biopsies in place of tissue-based ones. "That's the goal and the dream, but we still need to see how much it correlates with the results of natural biopsy."

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