The combination of two cancer drugs from UK-Swedish drugs maker AstraZeneca and its biologics research and development arm MedImmune could be a potential breakthrough in treating a form of lung cancer.

The companies have released results of their Phase IB study where durvalumab and tremelimumab were used to treat patients with progammed death-ligand 1 (PD-L1) negative tumors.

PD-L1 is a protein that is suspected of playing a major in suppressing the immune system. According to AstraZeneca, around two-thirds of patients with non-small cell lung cancer have PD-L1 negative tumors which respond less favorably to treatment than patients with PD-L1 positive tumors.

Initial results from the research were presented at the annual meeting of the Society for Immunotherapy in Cancer last November. The latest publication includes a more detailed analysis of the technique, with a longer follow-up period and more mature data set of confirmed responses.

Scott Antonia, chair of the Department of Thoracic Oncology at Moffitt Cancer Center in Florida, US, said the results suggest that the combination has potential as a treatment for patients with PD-L1 negative tumors whose needs are not addressed by currently available therapies, including immunotherapies.

Describing the new data as an important milestone, Ed Bradley, MedImmune’s senior vice president, oncology, added that the latest findings reinforced the belief that the combination strategy being pursued was key to the future success of immune-oncology treatment.

Durvalumab is an investigational human monoclonal antibody directed against PD-L1, while tremelimumab is a fully human anti-CTLA-4 antibody. Tremelimumab was granted orphan drug status by the US Food and Drug Administration in 2015.

Lung cancer is the leading cause of cancer-related death in both men and women and has a five-year survival rate of less than 20%.