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Inflammatory breast cancer (IBC) is an aggressive BC subtype with poor outcomes. A targetable somatic PIK3CA mutation is reported in 30% of IBC, allowing for treatment by PI3Kα-specific inhibitors, such as alpelisib. The aim of this study was to evaluate the detection rate of circulating PIK3CA mutation in locally-advanced IBC (LAIBC) patients harbouring a PIK3CA mutation on initial biopsy. This monocentric retrospective study was based on available stored plasma samples and tumour biopsies at diagnosis from all LAIBC patients treated with neo-adjuvant chemotherapy (NCT) between 2008 and 2018 at the Centre Henri Becquerel. PIK3CA mutations (E542K, E545K, H1047R/L) were assessed by droplet digital PCR (ddPCR) in plasma samples and tumoral tissue at diagnosis. A total of 55 patients were included. Overall, 14/55 patients (25%) had a PIK3CA mutation identified on baseline biopsy (H1047R = 8; H1047L = 3; E545K = 2; E542K = 1). Among them, 11 (79%) patients had enough DNA for circulating DNA analyses, and corresponding circulating PIK3CA mutations were found in 6/11 (55%). Among the 41 patients without PIK3CA mutations on biopsy, 32 (78%) had enough DNA for circulating DNA analysis, and no circulating PIK3CA mutation was identified. Our results revealed no prognostic or predictive value of PIK3CA mutations at the diagnosis of non-metastatic IBC but highlighted the prognostic value of the cfDNA rate at diagnosis. Our study showed that a corresponding circulating PIK3CA mutation was identified in 55% of LAIBC patients with PIK3CA-mutated tumours, while no circulating mutation was found among patients with PI3KCA wild-type tumours., (© 2021. The Author(s).)

Background: Endocrine therapy is recommended as a first-line treatment for hormone receptor-positive metastatic breast cancer (HR+MBC) patients. No biomarker has been validated to predict tumor progression in that setting. We aimed to prospectively compare the risk of early progression according to circulating ESR1 mutations, CA-15.3, and circulating cell-free DNA in MBC patients treated with a first-line aromatase inhibitor (AI)., Methods: Patients with MBC treated with a first-line AI were prospectively included. Circulating biomarker assessment was performed every 3 months. The primary objective was to determine the risk of progression or death at the next follow-up visit (after 3 months) in case of circulating ESR1 mutation detection among patients treated with a first-line AI for HR+MBC., Results: Overall, 103 patients were included, and 70 (68%) had progressive disease (PD). Circulating ESR1 mutations were detected in 22/70 patients with PD and in 0/33 patients without progression (p < 0.001). Among the ESR1-mutated patients, 18/22 had a detectable mutation prior to progression, with a median delay of 110 days from first detection to PD. The detection of circulating ESR1 mutations was associated with a 4.9-fold (95% CI 3.0-8.0) increase in the risk of PD at 3 months. Using a threshold value of 25% or 100%, a CA-15.3 increase was also correlated with progression (p < 0.001 and p = 0.003, respectively). In contrast to ESR1, the CA-15.3 increase occurred concomitantly with PD in most cases, in 27/47 (57%) with a 25% threshold and in 21/25 (84%) with a 100% threshold. Using a threshold value of either 25% or 100%, cfDNA increase was not correlated with progression., Conclusion: The emergence of circulating ESR1 mutations is associated with a 4.9-fold increase in the risk of early PD during AI treatment in HR+MBC. Our results also highlighted that tracking circulating ESR1 mutations is more relevant than tracking CA-15.3 or cfDNA increase to predict progression in this setting., Trial Registration: ClinicalTrials.gov, NCT02473120. Registered 16 June 2015-retrospectively registered after one inclusion (first inclusion 1 June 2015).

Purpose: To assess the prognostic and predictive value of circulating ESR1 mutation and its kinetics before and after progression on aromatase inhibitor (AI) treatment., Patients and Methods: ESR1 circulating D538G and Y537S/N/C mutations were retrospectively analyzed by digital droplet PCR after first-line AI failure in patients treated consecutively from 2010 to 2012 for hormone receptor-positive metastatic breast cancer. Progression-free survival (PFS) and overall survival (OS) were analyzed according to circulating mutational status and subsequent lines of treatment. The kinetics of ESR1 mutation before (3 and 6 months) and after (3 months) AI progression were determined in the available archive plasmas., Results: Circulating ESR1 mutations were found at AI progression in 44/144 patients included (30.6%). Median follow-up from AI initiation was 40 months (range 4-94). The median OS was decreased in patients with circulating ESR1 mutation than in patients without mutation (15.5 versus 23.8 months, P=0.0006). The median PFS was also significantly decreased in patients with ESR1 mutation than in patients without mutation (5.9 vs 7 months, P=0.002). After AI failure, there was no difference in outcome for patients receiving chemotherapy (n = 58) versus non-AI endocrine therapy (n=51) in patients with and without ESR1 mutation. ESR1 circulating mutations were detectable in 75% of all cases before AI progression, whereas the kinetics 3 months after progression did not correlate with outcome., Conclusion: ESR1 circulating mutations are independent risk factors for poor outcome after AI failure, and are frequently detectable before clinical progression. Interventional studies based on ESR1 circulating status are warranted.