MADRID (Reuters) – A new blood test from Roche and Foundation Medicine has shown it can accurately measure the number of mutations within a tumor, potentially helping doctors predict which patients may respond best to some immunotherapies.

Initial data on Roche’s new test aimed at determining tumor mutational burden, or TMB, was released on Friday at the European Society for Medical Oncology (ESMO) congress in Madrid. There are no TMB blood tests on the market now, Roche said.

Immunotherapies like Roche’s Tecentriq, Merck’s Keytruda and Bristol-Myers Squibb’s Opdivo have offered fresh hope to people with deadly cancers, but they only work in a fraction of patients.

And given immunotherapies’ high costs and possible serious side effects, with British regulators having dubbed Tecentriq too pricey, doctors want better ways of figuring out which patients would benefit the most from such treatments.

Evidence shows that tumors with more mutations are more likely to respond to immunotherapy, Roche said, adding that it hoped its and Foundation’s new test would improve measuring TMB where invasive tumor biopsies that can be tough to evaluate are now required.

“Biomarkers will not only improve our understanding of immune biology but will ultimately help match our therapies and combinations to the people most likely to benefit,” said Sandra Horning, MD, Roche’s chief medical officer.

”This blood-based TMB assay is one example of how we and our partners are advancing the science towards personalization of cancer therapy.”

The biomarker data being presented at ESMO was gathered using nearly 800 plasma samples from patients in Roche’s studies of its drug Tecentriq for treating lung cancer.

The Basel-based company also has a pair of prospective studies underway in lung cancer patients to evaluate and validate its TMB test.

Roche, which owns 58 percent of Foundation, is developing 20 cancer immunotherapy medicines across nine types of cancer, both by themselves and in combination with dozens of other drugs.