Abstract P2-11-02: BIOMARKERS RELATED TO SURVIVAL BENEFIT IN THE TREATMENT OF METASTATIC LUMINAL BREAST CANCER (mBC) WITH CYCLIN 4/6 INHIBITORS (CDK 4/6i) PLUS ENDOCRINE THERAPY (ET)

Abstract Treatment with CDK4/6i plus ET is the standard treatment for mBC with a significantly better progression free survival (PFS) and a long treatment duration response, although there’s finally a progression. The expression of cyclin E and progesterone receptor had been related to survival, so analyzing of these potential biomarkers could help to select their effect in patients with a long treatment duration (> 20 months). We evaluate 68 mBC treated with CDK4/6I plus ET as a clinical practice in a single institution. Median age was 68 years, 27(39,7%) patients had de novo metastatic disease, 17 (25%) progressed during ET adjuvant, and 24 (35,3%) progressed after 5 years of ET. Forty-eight patients (70%) received CDK4/6I plus ET in first line and visceral disease was present in 40% of patients. The median expression by histoscore with immunohistochemistry of cyclin E (CycE) was 75,3 (4-97) and progesterone receptor (PR) 121. Median PFS was 16 months (8,3- 23,6) with 45 events, 25 months in patients treated in first line and 12 months in second line (p: 0,0001). We analyzed 59 patients who had already completed CDK4/6I plus ET or had achieved a PFS more than 20 months, 40 (69%) in first line and 18 (31%) in second line. We summarized the related of expression of PR, CycE and this combination with PFS more than 20 month. CONCLUSION: Treatment with CDK4/6i plus ET achieved long treatment duration in patients with low expression of cyclin E (OR 3,1 p:0,045), positive progesterone receptor (OR 3,89 p: 0023) and specially in patients with positive progesterone receptor and low expression of cyclin E (OR 7,22 p:0,016). Patients with negative progesterone receptor and high expression of cyclin E had a poor prognosis with a median disease-free survival of 6 months (2.8 – 9.2), so these patients required other treatment approaches to improve their outcomes. Table Citation Format: Serafin Morales Murillo, Ariadna Gasol Cudós, Noemí Tuset Der-Abrain, Izaskun Urdanibia, Alvaro Rodriguez Galindo, Ana Velasco Sánchez, Felip Vilardell Villellas, Douglas Sánchez Guzmán, Carles Canosa Morales, Jordi Melé Olivé, Laura Arbones Cid. BIOMARKERS RELATED TO SURVIVAL BENEFIT IN THE TREATMENT OF METASTATIC LUMINAL BREAST CANCER (mBC) WITH CYCLIN 4/6 INHIBITORS (CDK 4/6i) PLUS ENDOCRINE THERAPY (ET) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-11-02.