Abstract PD2-06: Circulating ESR1 mutation detection rate and early decrease under first line aromatase inhibitor and palbociclib in the PADA-1 trial (UCBG-GINECO)

Abstract

Background: Palbociclib (Pal) combined with an aromatase inhibitor (AI) is a standard of care as first line therapy in ER+ HER2- metastatic breast cancer (MBC). While ESR1 mutations (ESR1mut) are a characterized mechanism of resistance to AI as single agent, it remains unknown how these mutations, when detected prior to treatment initiation, may affect the efficacy of Pal+AI. In a subsidiary analysis of the first line PADA-1 trial, we report the ESR1mut detection rate at baseline and, in patients with ESR1mut detected at baseline, how ESR1 circulating tumor DNA levels changed after the first cycle of AI-Pal therapy. Methods: PADA-1 (NCT03079011) is a randomized phase III trial testing the clinical utility of real time ESR1mut detection (baseline, at 1 month and then every 2 months) in the blood of patients treated with AI-Pal (first step). Patients with rising ESR1mut in circulating tumor DNA (i.e. increasing or appearing mutations during first line AI-Pal therapy) are randomized in a second step between keeping AI-Pal or switching to Fulvestrant-Pal. Main inclusion criteria are patients with ER+ HER2- MBC, who never received adjuvant AI or completed adjuvant AI for >12 months, with neither prior therapy for MBC nor visceral crisis. ESR1mut are tracked in circulating DNA from up to 4ml of plasma by a ddPCR-based assay targeting E380, L536, Y537 and D538 hotspots (i.e. #90% of known ESR1 activating mutations) with #0.1% sensitivity (Bidard et al, AACR 2018 #3867). Results: From 04/2017 to 05/2018, 803 MBC patients have been included in 80 centers. Among these patients, ESR1mut were detected at baseline, prior to any systemic therapy, in 17 patients (2.1%, 95%CI=[1.3;3.3%]). ESR1mut levels ranged from 6 to 3959 copies/ml of plasma (median: 30 copies/ml); allelic frequency ranged from 0.3% to 47% (median=3.5%). ESR1mut were not associated with any of the tumor pathological characteristics (including PR status, primary TNM stage, number and type of metastatic sites); a non-significant association was observed with primary tumor grade (1.7% vs 4.1% in grade I-II vs III, Fisher: p=0.15). Among patients who received a prior adjuvant endocrine therapy, ESR1mut detection rate was lower in patients treated with tamoxifen (0.9% with any tamoxifen exposure vs 5.7% with no tamoxifen exposure; Yates Chi2: p=0.01) and observed only in patients treated with AI (4.9% with any AI exposure vs 0% with no AI exposure, Yates Chi2: p=0.009). Among the 17 patients with ESR1mut detected at baseline, only 4 patients had residual detectable ESR1mut detected after 1 month of AI-Pal therapy (3 of these 4 had decreased levels of ESR1 mutation). Conclusion: ESR1mut is a rare event in untreated AI-sensitive, ER+ HER2- MBC patients. Such detection is primarily associated with prior use of AI in the adjuvant setting. Interestingly, in most MBC patients with ESR1mut detected at baseline, ESR1mut became undetectable after 1 month of AI-Pal therapy, suggesting that this combination may retain early antitumor efficacy. Funding: Pfizer Citation Format: Bidard F-C, Pistilli B, Dalenc F, De la Motte Rouge T, Sabatier R, Frenel J-S, Ladoire S, Dubot C, Ferrero J-M, Levy C, Lortholary A, Stefani L, Mouret-Reynier M-A, Hardy A-C, Jacquin J-P, Grenier J, Chakiba C, Teixeira L, Soulie P, Everhard S, Lemonnier J, Jeannot E, Bieche I, Berger F, Pierga J-Y, Bachelot T, Delaloge S. Circulating ESR1 mutation detection rate and early decrease under first line aromatase inhibitor and palbociclib in the PADA-1 trial (UCBG-GINECO) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD2-06.

Identification of cell surface targets for CAR-T cell therapies and antibody–drug conjugates in breast cancer

“… 20 The identification of different molecular subtypes and their prognostic role is already changing the therapeutic decision making 14 ; molecular subtyping, genomic and mutational profiling in tumor tissue or liquid biopsy is also driving the development of innovative clinical trials for both the early and advanced disease. 21 , 22 , 23 , 24 Within this innovative scenario, where the old ‘one-size-fits-all’ paradigm is rapidly shifting toward a patient-centered, biomarker/genetic-driven personalized therapeutic approach, the need to find new personalized treatment strategies is crucial. What makes this a hard task, among other issues, is the vast amount of available scientific information, sometimes contradictory, sometimes incomplete or very preliminary, which implies time-consuming, potentially expensive and prone-to-bias subjective evaluation of preclinical research with the objective of discovering new potential therapeutic targets and treatment strategies that could adapt to specific patient populations or diseases with specific molecular characteristics.…”

Circulating tumor DNA analysis in breast cancer: Is it ready for prime-time?

“…Preliminary results showed a detection rate of 2.1% at baseline, with an allelic frequency ranging from 0.3% to 47% (median = 3.5%). Notably, among the 17 patients with baseline ESR1 mutations, only 4 had detectable ESR1 mutations after 1 month of therapy [110].…”

Liquid Biopsy: New Tool to Overcome CDKi Resistance Mechanism in Luminal Metastatic Breast Cancer

“…As preliminary results, ESR1 mutations were uncommon in patients no-treated with AI in the neoadjuvant setting. Besides, one-month treatment with palbociclib and AI decreases ESR1 mutation rate [57], [58].…”