Presentation of the PALOMA-1 trial results represented “the culmination of a long journey from the discovery of cyclin-dependent kinase (CDK) 4/6 in the early 1990s,” said José Baselga, MD, PhD, Physician-in-Chief at Memorial Sloan Kettering Cancer Center, New York. Dr. Baselga was formal discussant of the trial presented by Finn et al at the American Association for Cancer Research Annual Meeting. “These strikingly positive results have a large potential to impact patients with breast cancer. If these results are confirmed, a CDK4/6 inhibitor plus endocrine therapy could be a new standard of care for metastatic breast cancer,” he said.

“The elephant in the room,” Dr. Baselga continued, “is that highly positive randomized phase II studies that are open label and that have investigator- based assessment of progression-free survival can be followed by negative phase III trials,” so the results need to be validated by further study. Palbociclib plus letrozole is going forward with phase III testing in the PALOMA-2 trial, and results of that study will be eagerly awaited.

Breast cancer is a fertile area of research for CDK4/6 inhibitors, Dr. Baselga continued. Other CDK4/6 inhibitors are under study. Lilly’s compound LY2835219 had striking early results reported at this year’s AACR Annual Meeting and Novartis’ LEE011 is being evaluated in the phase III MONALEESA trial. ■

Disclosure: Dr. Baselga is a consultant for Elli Lilly, Novartis, Genentech, Verastem, and Seragon.