Abstract PO2-05-07: Which treatment is done in patients with metastatic breast cancer who received a prior treatment with CDK4/6 inhibitors? A real-world experience in a single italian Institution

Abstract Patients with HR positive (HR+) and c-erb-b2 negative (HER2-) advanced breast cancer are treated with cyclin-dependent kinase 4/6 (CDK4/6) inhibitors in combination with hormone therapy (HT). At the time of disease progression with these treatments, no established guidelines are defined for the subsequent therapeutic options.Treatment options after progression can be different, in terms of use of chemotherapy or ET alone, or the combination of the two, or of other biological agents (such as everolimus) or the HT combined with other therapies. We aimed to verify in our Institute (IRCCS Istituto Romagnolo per lo Studio dei Tumori (IRST) "Dino Amadori", Meldola, Italy) how HR+ mBC patients are treated after having received a treatment with HT plus CDK4/6 inhibitors (ribociclib, palbociclib, abemaciclib). 105 mBC patients, 32 of whom were treated with CD4/6 inhibitors plus letrozole and 73 treated with CDK4/6 inhibitors and fulvestrant were included in the study. 83 were treated with palbociclib, 16 with ribociclib and 6 with abemaciclib. The median age was 65 years (range 40-86), 58 were younger than 65 years. 90 were in postmenopausal status. On the total 105 patients, 46 (43.8%) were treated with a single chemotherapy regimen while 25 (23.8%) with a combined schedule of chemotherapies (Table 1). Only 9 (8.6%) have been treated with HT alone. 22 (20.95%) patients received combined treatments with ET or chemotherapy+targeted therapy or chemotherapy +immune checkpoint inhibitor. 1 (0.95%) patients was treated with a triplet chemotherapy regimen (cyclophosphamide+capecitabine +vinorelbine), 2 (1.9%) for whom the re-biopsy of the tumor resulted HER2 + were treated with taxol +pertuzumab +trastuzumab. 82/105 (78%) patients performed more lines of therapies after CDK4/6 inhibitors. In conclusion, patients with mBC were treated heterogeneously. The major part of them have been treated with chemotherapy alone or with combination of more chemotherapies. The evaluation of the patient response in relation to the different therapies is still ongoing as well as the effect of all the other therapies beyond the first line of treatment. Table 1. Type of treatments done in mBC patients (Nf105) after treatment with HT+ CDK4/6 inhibitors *1 performed only 1 cycle ** 1 was treated also with a metronomic schedule of therapy Citation Format: Sara Bravaccini, William Balzi, Andrea Roncadori, Alessandra Virga, Paola Ulivi, Giovanni Martinelli, Roberta Maltoni. Which treatment is done in patients with metastatic breast cancer who received a prior treatment with CDK4/6 inhibitors? A real-world experience in a single italian Institution abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-05-07.