Researchers Identify Marker on Tumor Cells That Predicts Response to Immunotherapy

Researchers at the Mass General Brigham Cancer Institute found that a “particular marker on tumor cells circulating in the blood indicates whether a patient with lung cancer will experience a lasting response to a newly approved immunotherapy called tarlatamab.”

The senior author of the study, Daniel A. Haber, said that the practice of “isolating cancer cells from the blood has tremendous potential to guide immune-related cancer therapies.”

The study focused on “whether properties of circulating tumor cells might correlate with a patient’s response to tarlatamab, which was fully approved in late 2025 as a treatment for small cell lung cancer (SCLC) after prior chemotherapy. Tarlatamab is an antibody that recruits T cells to cancer cells expressing a specific neuro-endocrine marker called DLL3.” Around half of patients with SCLC experience cancer progression within six months of starting therapy.

The researchers found that “only half of the 20 patients they studied had abundant DLL-3 positive cancer cells in their blood, and these were the patients who responded to tarlatamab. DLL3 testing on CTCs correctly identified 85% of patients who had a clinical benefit from the drug and 100% who did not (85% sensitivity, 100% specificity).”