A domestic research team has developed a potential for a new biomarker – raising the possibility of developing a new treatment method.

Immunotherapies are becoming a new treatment method for patients not responsive to existing anticancer treatments. However, medical evidence regarding which immunotherapies are effective for which patients were lacking.

A research team led by four professors from Samsung Medical Center - Kang Won-ki, Lee Jee-yun, Kim Seung-tae and Kim Kyung – has set out to identify the determinants of immunotherapy response.

The team conducted the two-year study and confirmed the effect of Keytruda (pembrolizumab) on 61 patients with metastasized gastric cancer by administering it to patients who were unresponsive to existing therapies

Nearly half, or about 30 people, had their cancer cells reduced in the study. Of them, 15 patients had more than 30 percent of their tumors cut down. Five patients had more than 75 percent of their tumors slashed.

All patients who showed a response to the immunotherapy had the programmed death-ligand 1 (PD-L1) protein. PD-L1 plays a significant role in suppressing the immune system and is found on the surface of cancer cells.

The research team conducted a genetic analysis on 57 patients to uncover the similarities among patients who showed a response to the immunotherapy and had their tumors reduced. Researchers thereby found several characteristics of these patients that were previously not discovered.

All six patients who had a tumor reduction rate exceeding 30 percent were positive for the Epstein–Barr virus (EBV), genetic analysis showed. Five out of six patients who also had the Microsatellite instability (MSI-High) displayed a tumor reduction of about 50 percent.

“In patients with MSI-High and Epstein–Barr virus-positive tumors, which are mutually exclusive, dramatic responses to pembrolizumab were observed,” the researchers wrote.

Meanwhile, gastric cancer patients who had an Epithelial-mesenchymal transition (EMT) showed a weaker response to immunotherapy regardless of whether they were PD-L1 positive.

Researchers stated their plans to develop new biomarkers and to develop new drugs that raise the response to immunotherapies.

“Knowing in advance which treatments will be effective for advanced gastric cancer patients allows physicians to tailor a treatment strategy accordingly,” the research team said. “Ultimately, this will contribute to raising the survival rate for patients with metastasized gastric cancer by opening the door to precision medicine.”

The study was published in the recent issue of Nature Medicine.