Abstract P5-02-17: Concordance Analysis of Non-Invasive determination techniques of PIK3CA and ESR1 mutations in patients with advanced luminal breast cancer. Study CANIPE

Abstract

Abstract Approximatly 70% of breast cancer (BC) patients are Hormone Receptors (HR) positive, the most common subtype with the best prognosis. The combination of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) with Endocrine Therapy (ET) is tje standard firs-line therapy for HR+/HER2- metastatic BC. However, 20% of patients are intrinsically resistant, and those who initially respond often develop acquired resistance, making the management of resistant HR+/HER2- metastatic BC a significant clinical challenge. Clinical guidelines emphasize the need of comprehensive real-time monitoring of the dynamic mutational landscape during and after treatment to improve resistance prediction. Early detection of mutations in ESR1 and the PIK3 pathway usinf circulating tumor DNA (ctDNA) may allow the ending of ineffective endocrine therapies and initiation of alternative treatments for these patients, without performing tissue biopsies before radiological progression occurs. To achieve this, it is crucial to implement non-onvasive genotyping that allows better-adapted pharmacologiical interventions. However, clinical trials have been predominantly carried out with selected populations and single drugs (Palbociclib, Ribociclib or Abemaciclib). There is a lack of studies of optimal agreemnt between diagnostic methods, especially in liquid biopsy. There is no relieble data abaout PIK3CA or ESR1 status in ctDNA from real-world cohorts that could help to define the best testing strategy for the clinica routine. Therefore, it is imperative to establish evidence that the use of ddPCR is equally or more sensitive for ctDNA analysis than qPCR or NGS, the current gold standard methods. Aim: This study aims to perform a concordance analysis between NGS and ddPCR technologies for detecting mutations in PIK3CA and ESR1 by testing the ctDNA from HR+/HER2- metastatic breast cancer patients. M&M: CANIPE is a randomised, open-label study performed al 14 Spanish hospitals in 6 autonomous communities. Patients aged 18 years or older, with confirmed HR+/HER2- breast cancer, stage IV, Eastern Cooperative Oncology Group performance status (ECOG-PS) of 0 to 2, who iniciate first-line tratment with CDK4/6i plus aromatase inhibitors. All procedures followed the Helsinki Declaration guidelines and were approved by the Ethics Commitee of Santiago-Lugo under approval reference number 2022/386. All patients provide written informed consent. A total of 60 women were recruited at baseline (before therapy initiation) while 21 patients at 10 months after treatment. 40 mL of blood was obteined from each patient at both time points. For ddPCR, cfDNA was isolated from 5 mL of plasma using the QIAamp Circulating Nucleic Acid Kit (Qiagen, Venlo, The Netherlands). Multiplex ddPCR was performed with de Bio-Rad QX-200 system to identify PIK3CA mutations, including the most frequent variants (E542K, E545K, H1047L, H1047R, R88Q, N345K, C420R, E545A, E545G,Q546K), and ESR1 mutations (L536R, D538G, E380Q, Y537C, /537S, Y537N,S463P). A mutation was considered present if at least 6 mutated events were detected by ddPCR. Additionally, for NGS, cfDNA was isolated from 4 mL of plasma and analysed with the AVENIO ctDNA Expanded kit (Roche Diagnostics), which includes 77 genes, including PIK3CA and ESR1. An allele fraction od 0.5 % or higher was consideredindicative of a mutation. Results: At baseline, and considering the pre-defined criteria, ctDNA analysis detected PIK3CA mutations in 32.25% and 44.44% of patients by AVENIO and ddPCR, respectively. ESR1 mutations were detected in 3.22% and 9.37% by AVENIO and ddPCR, respectively. For PIK3CA mutations, the Kappa value was 0.62 (p-value: 0.0004) and 0.47 for ESR1 mutations (p-value: 0.0039). However, when NGS data was included for mutations with allele fraction less than 0.5%, the Kappa value was 0.92 for PIK3CA and 1 for ESR1, indicating almost perfect agreement bvetween the two technologies (p-value < 0.0001). Conclusion: The analysis of ctDNA bu Multiplex ddPCR of HR+/HER2- metastatic breas cancer patients represent a sensitive tool to identify PIK3CA and ESR1 mutations with a high concordance compared with the NGS, which is currently the reference technology. Citation Format: Teresa Curiel, Carmela Rodriguez, Aitor Rodriguez Casanova, Nerea González, Ramón Lago-Lestón, Martín Giráldez, Alicia Abalo, Carmen Abuín, Maribel Aibar, Patricia Palacios, Juan Cueva, Marta carmona, Alexia Cortegoso, Serafín Morales, Josep Gumá, Mariana López Flores, Yolanda Fernández, Isaura Fernádez, Ignacio Fernández, María Gión, Carolina Pena, Jesús García Mata, Andrea Saenz de Miera, Angel Díaz Lagares, Laura Muinelo Romay, Clotilde Costa, Rafael López López. Concordance Analysis of Non-Invasive determination techniques of PIK3CA and ESR1 mutations in patients with advanced luminal breast cancer. Study CANIPE [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P5-02-17.