After failing to significantly extend survival in a confirmatory Phase 3 trial, Keytruda (pembrolizumab) will no longer be available in the U.S. for people with previously treated metastatic small cell lung cancer (SCLC). According to Merck, known as MSD outside North America, the company decided to voluntary withdraw this indication after consulting with the U.S. Food and Drug Administration (FDA). The process will be complete in the coming weeks. Healthcare professionals are being informed of the company’s decision. Patients with metastatic SCLC in the U.S. who are currently using Keytruda should discuss treatment options with their doctors. This decision regarding these advanced SCLC patients does not affect other indications for which Keytruda is currently approved, both within and outside the U.S. “Keytruda remains a foundational treatment for certain patients with metastatic non-small cell lung cancer," Roy Baynes, MD, PhD, senior vice president and head of global clinical development, chief medical officer, Merck Research Laboratories, said in a press release. "We will continue to rigorously evaluate the benefits of Keytruda in small cell lung cancer and other types of cancer, in pursuit of Merck’s mission to save and improve lives,” Baynes added. Keytruda belongs to a class of medications known as immune checkpoint inhibitors, which block the activity of proteins often hijacked by cancer cells to dampen immune responses. By inhibiting one such protein, PD-1, Keytruda is believed to boost the immune system's ability to recognize and eliminate cancer cells. Keytruda received a conditional approval from the FDA in 2019 to treat advanced SCLC patients whose cancer was progressing despite two or more prior lines of therapy. The approval was based on promising response and duration rates observed in the KEYNOTE-028 Phase 1b (NCT02054806) and the KEYNOTE-158 Phase 2 (NCT02628067) trials. “The accelerated pathways created by the FDA have been integral to the remarkable progress in oncology care over the past five years and have helped many cancer patients with advanced disease, including small cell lung cancer, access new treatments,” Baynes said. However, Keytruda’s continued and full approval for this indication was dependent on confirmation of these benefits in a larger clinical trial. Merck designed the KEYNOTE-604 Phase 3 trial (NCT03066778) as that confirmatory study. It investigated whether Keytruda plus standard chemotherapy would improved the outcomes of newly diagnosed SCLC patients compared with chemotherapy only. KEYNOTE-604 met one of its two primary goals, with Keytruda extending the time patients lived without disease worsening from a median of 4.3 to 4.5 months. Patients on Keytruda also lived longer (10.8 months) than those on chemo only (9.7 months), but these differences in overall survival failed to reach statistical significance.