Adding a minimally invasive laser procedure to immunotherapy achieved dramatically improved survival in a small study of patients with recurrent high-grade astrocytoma, an aggressive brain cancer with few treatment options.

High-grade astrocytoma almost always returns after surgery. Patients with recurrent disease typically live another four to five months.

In a study of 45 patients with advanced recurrent high-grade astrocytoma, 42% of the 33 who received laser interstitial thermal therapy (LITT) to shrink their tumors, followed by Merck’s immunotherapy drug Keytruda, were still alive at 18 months, and more than one-third lived more than three years.

None of the six patients who received conventional surgery followed by Keytruda were alive at the 18-month mark, according to a report of the study in Nature Communications.

“Patients with this type of advanced cancer have few remaining options and poor outcomes, and this approach could meaningfully extend their survival time and provide new hope for patients and their loved ones,” study leader Dr. David Tran from the University of Southern California said in a statement.

The randomized study was stopped early by an independent data and safety monitoring committee when the benefit of LITT developed by Monteris Medical became obvious. Such committees can halt trials before their conclusion if it becomes clear the drug or device being tested is clearly beneficial and should also be given to the control group, or if it raises safety concerns or is providing no benefit.

Drugs like Keytruda that use the immune system's T cells to attack cancer are approved for many types of the disease, but generally fail in brain tumors because the blood-brain barrier prevents them from reaching the intended target.

Researchers in earlier studies had seen that the heat produced by LITT can disrupt the blood–brain barrier for several weeks – long enough for T cells to pass through and target cancer cells once they have been activated by Keytruda.

Larger studies are needed before this can become a standard treatment, the researchers noted.