AstraZeneca PLC said its drug Imfinzi showed long-term promise in a phase 3 clinical trial in patients with stage 3 non-small cell lung cancer whose tumors cannot be removed through surgery.

Three-year results from the Pacific study showed the drug extended patients' lives longer than placebo in lung cancer patients whose diseases had not progressed following concurrent chemoradiation therapy.

"These three-year survival results further establish the Pacific regimen as the standard of care for these patients, and we are optimistic that this survival trend will continue as we move toward the five-year landmark in this curative-intent setting," said Dave Fredrickson, executive vice president of oncology business.

Stage 3 NSCLC, which means the disease has spread into nearby tissues, affects about 43,000 patients in the U.S. The majority of patients with the disease have tumors that cannot be removed through surgery.

The U.K. drugmaker's Imfinzi, or durvalumab, is part of a class of tumor-targeting drugs called checkpoint inhibitors. The drugs block the PD-L1 protein on cancer cells from linking with a partner arm on healthy cells — an interaction that prevents the spread of the disease.

The post-hoc analysis of the trial data showed that showed that overall survival, or the length of time a person stays alive with the disease, was 57% at three years for patients given Imfinzi compared to 43.5% for those taking placebo following concurrent chemoradiation therapy. The median overall survival was not yet reached with patients taking Imfinzi, while median OS was 29.1 months for the placebo group.

The Pacific study previously met its main goals of overall survival and progression-free survival, or the length of time a patient stays alive without the disease getting worse.

In the previous two-year overall survival analysis, Imfinzi was shown to cause side effects of cough, fatigue, dyspnea and radiation pneumonitis in over 20% of patients. 30.5% of patients taking Imfinzi experienced a grade 3 or 4 adverse effect compared with 26.1% of those taking placebo.

The Imfinzi group also saw 15.4% of patients stopping treatment due to adverse events compared with 9.8% of patients discontinuing treatment in the placebo group. 713 patients participated in the Pacific trial.

Imfinzi is already approved in 45 countries and territories, including the U.S., EU and Japan, based on the results of the Pacific trial.

The 2019 American Society of Clinical Oncology meeting is expected to bring together more than 32,000 professionals from around the world, with more than 2,400 study abstracts to be presented on site and an additional 3,200 abstracts to be published online.