Abstract PO2-15-06: ctDNA-based DNADX in hormone receptor-positive and HER2-negative (HR+/HER2-) advanced breast cancer following endocrine therapy and CDK4/6 inhibition: a correlative analysis from the randomized phase 2 PARSIFAL trial
Authors: Brasó-Maristany Fara , Cortés Javier , Pérez-García José Manuel , Vega-León Rosario , Paré Laia , Villacampa Guillermo , Matito Judit , Pardo Francisco , Gomez-Rey Marina , Mancino Mario , Martínez-García Elena , Gallardo Carmen Mora , Mina Leonardo , Dalenc Florence , Ezquerra Meritxell Bellet- , Ruíz - Borrego Manuel , Gil-Gil Miguel , Schmid Peter , Perou Charles M. , Parker Joel S. , Villagrasa Patricia , Vivancos Ana , Prat Aleix , Llombart-Cussac Antonio 
Published: May 2024

ctDNA-based DNADX in hormone receptor-positive and HER2-negative (HR+/HER2-) advanced breast cancer following endocrine therapy and CDK4/6 inhibition: a correlative analysis from the randomized phase 2 PARSIFAL trial Background: DNADX, a novel machine learning-based approach, utilizes DNA from tumor tissue or plasma ctDNA to identify clinically relevant phenotypic tumor features and classify breast cancer into 4 subtypes (Nat Comm 2023). Here, we evaluated DNADX's ability to predict prognosis and treatment benefit in HR+/HER2- advanced breast cancer following endocrine therapy and a CDK4/6 inhibitor. Methods: DNADX was evaluated centrally in available baseline plasma ctDNA samples from PARSIFAL trial (NCT02491983) which randomized 486 patients (pts) with HR+/HER2- advanced breast cancer to receive (1:1 ratio) first line palbociclib with either fulvestrant or letrozole. Shallow whole genome sequencing was performed on ctDNA, and the 4 DNA-based subtypes (Clusters-1, -2, -3, and -4) were identified if the ctDNA tumor fraction (TF)≥3%. The main objective was to evaluate the association of DNADX subtypes with progression-free survival (PFS) and overall survival (OS). Secondary objective was to identify the subgroup of pts who benefit more from each endocrine treatment. Uni- and multi-variable Cox regression models were used after adjusting for TF, menopausal status, ECOG status, de novo metastasis (vs. recurrence), visceral disease and number of metastatic sites. Results: DNADX was evaluated in plasma ctDNA samples from 122 pts (25.1%). Clinical variables and median PFS (27.6 months) were similar as the overall PARSIFAL population. DNADX identified 56.6% pts with TF of &lt; 3%, 14.8% with Cluster-1, 19.7% with Cluster-2, 5.7% with Cluster-3 and 3.3% with Cluster-4. In terms of PFS, pts classified with TF&lt; 3% had a lower risk of progression compared to Cluster-1, Cluster-2, Cluster-3, Cluster-4 subtypes (pairwise PFS hazard ratios [HRs] of 1.88, 2.02, 3.15, and 5.62, respectively, with a global log-rank test of p=0.010). Similar results were obtained after adjusting for other clinical-pathologic variables. A numerical benefit of fulvestrant in comparison with letrozole was observed in pts classified in Cluster-1 and Cluster-4 (HR=0.42, 95% CI 0.14-1.24) in contrast to the other groups (HR=1.21, 95% CI 0.68-2.18), and the interaction test was statistically significant after adjusting for clinical-pathologic variables (anova p-value=0.037). In terms of OS, pts classified with TF&lt; 3% had a lower risk of death compared to Cluster-1, Cluster-2, Cluster-3, and Cluster-4 subtypes (pairwise OS HRs of 1.90, 4.23, 11.13, and 6.80, respectively, with a global log-rank test of p=0.003). In the multivariable analysis, results were consistent after adjusting for clinical-pathologic variables and TF. Conclusions: Liquid biopsy-based DNADX subtypes predict outcomes in pts with HR+/HER2- advanced breast cancer on endocrine therapy and CDK4/6 inhibitors, potentially identifying the most optimal endocrine treatment for each pt.

Citation Format: Fara Brasó-Maristany, Javier Cortés, José Manuel Pérez-García, Rosario Vega-León, Laia Paré, Guillermo Villacampa, Judit Matito, Francisco Pardo, Marina Gomez-Rey, Mario Mancino, Elena Martínez-García, Carmen Mora Gallardo, Leonardo Mina, Florence Dalenc, Meritxell Bellet- Ezquerra, Manuel Ruíz - Borrego, Miguel Gil-Gil, Peter Schmid, Charles M. Perou, Joel S. Parker, Patricia Villagrasa, Ana Vivancos, Aleix Prat, Antonio Llombart-Cussac. ctDNA-based DNADX in hormone receptor-positive and HER2-negative (HR+/HER2-) advanced breast cancer following endocrine therapy and CDK4/6 inhibition: a correlative analysis from the randomized phase 2 PARSIFAL trial [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 PO2-15-06.