Initial results from the Canarian registry of luminal breast cancer patients treated with first-line CDK 4/6 inhibitors

CDK 4/6 inhibitors have revolutionized the treatment of HER2-negative luminal breast cancer, with median progression-free survival (PFS) of over 25 months and overall survival (OS) of over 60 months. After more than five years since their commercialization in our country, the Canarian Breast Cancer Group decided to analyze the results obtained in our region. We collected data on the characteristics of patients treated with cyclin inhibitors in the first line, including their diagnosis, treatment, and evolution, in the 7 oncology centers across the archipelago. From January 2017 to December 2022, 583 patients were registered, median age of 60 y. Of these, 65% had relapsed, with 30% relapsing more than one year after completing adjuvant hormonal therapy (HT) and the remaining 35% relapsing during the HT. The median PFS was 15 months, in de novo patients and in those who had completed HT more than one year before was 20 months. The OS was 52 months, in de novo patients having a higher OS of 58 months. Patients treated with abemaciclib tended to have higher PFS and OS rates in cases of hormone resistance and visceral disease. No differences were found in patients diagnosed under 50 years of age. Our patients experienced lower PFS and OS rates than those reported in clinical trials, which may be due to a higher number of patients exposed to HT and up to 46% of patients presenting with visceral disease at diagnosis. Further follow-up is required to confirm differences between cyclin inhibitors.