The drug has shown early potential as an effective treatment for non-small cell lung cancer, the leading cause of cancer death among men and women worldwide.
Dr Edward Garon, director of thoracic oncology at University of California, Los Angeles (UCLA), presented the preliminary results of a Phase 1B study of the new drug, called MK-3475.
The detailed interim data on safety and activity came from a cohort of 38 patients with non-small cell lung cancer who were treated previously for the disease without positive results. For the study, the patients received MK-3475 every three weeks.
For those who responded, the median response duration - the average amount of time their tumours remained shrunk - had not been reached at the time of this analysis, so it is at least 62 weeks.
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Based on this data, a Phase 2/3 trial comparing two different doses of MK-3475 to standard chemotherapy for lung cancer has begun enrolling patients.
Some cancer cells can evade detection by the immune system by expressing a protein called PD-L1, which interacts with the protein PD-1 to prevent the immune system from seeing the cancer as an invader.
The most commonly reported drug-related side effects in the study were of low grade.
"These are early results, but we are very encouraged by what we've seen so far with this drug," Garon said.