Abstract PS2-09-26: Circulating microRNA and cytokine signatures associated with interstitial lung disease in patients treated with trastuzumab deruxtecan

Abstract Background: Interstitial lung disease (ILD) is a clinically relevant adverse event associated with trastuzumab deruxtecan (T-DXd) in HER2-positive and HER2-low metastatic breast cancer. Most ILD cases are low grade, but severe forms can occur, particularly if diagnosis is delayed. To better understand the biology of T-DXd-related ILD, we conducted a translational study analyzing circulating microRNAs (miRNAs) and cytokines at the time of ILD diagnosis, comparing patients who developed ILD (cases) with those who did not (controls). Other anticancer agents, including mTOR and CDK4/6 inhibitors, have also been linked to ILD. Since these therapies are often administered sequentially during the disease course, an exploratory cohort of ILD cases from non-T-DXd treatments was also included to characterize potential shared or treatment-specific molecular signatures. Methods: We conducted a prospective, single-center case-control translational study including patients with HER2-positive or HER2-low metastatic breast cancer treated with T-DXd. The primary objective was to characterize circulating miRNA and cytokine profiles in patients who developed ILD (cases) compared with those who did not (controls). Controls were matched 1:1 by treatment duration and tumor subtype (HER2+ or HER2-low). An exploratory cohort included ILD cases attributed to other anticancer agents (everolimus and abemaciclib) administered sequentially during the disease course. Plasma samples were collected at the time of ILD diagnosis or at an equivalent treatment cycle for controls. ILD diagnosis was made at the investigator’s discretion and graded according to CTCAE version 5.0. miRNA expression was analyzed using the NanoString nCounter® Human v3 miRNA panel, and cytokine levels were measured using LEGENDplex™ multiplex immunoassays targeting immune response and checkpoint markers. Differential expression analyses were performed across cohorts. Results: 12 ILD cases and 12 matched controls treated with T-DXd were included. Mean age was 62.7 vs 57.4 years, with balanced distribution of tumor subtype (HER2-positive vs HER2-low), treatment duration, and baseline clinical characteristics. Differential expression analysis identified 11 overexpressed and 5 underexpressed plasma miRNAs in ILD cases compared to controls (p<0.005) (Table 1). Among the underexpressed miRNAs, hsa-miR-n and hsa-miR-o have been associated with inflammatory pathways, as well as hsa-miR-a, which is overexpressed. However, hsa-miR-q and hsa-miR-p, found underexpressed, are linked to fibrotic processes. Cytokine profiling showed increased levels of IL-6, CXCL10 and IFN-γ; and lower levels CCL2 in ILD cases. Inverse expression patterns were observed between selected miRNAs and cytokines: hsa-miR-a and CCL2, hsa-miR-n and IL-2, hsa-miR-q and Tim-3. In the exploratory cohort (n = 6; 3 everolimus, 3 abemaciclib), hsa-miR-m, hsa-miR-n and hsa-miR-o were underexpressed; while hsa-miR-a, hsa-miR-b and hsa-miR-c were overexpressed, which correlates with the expression profile observed in T-DXd-related ILD. Conclusions: This is the first study to characterize circulating microRNA and cytokine profiles associated with ILD in patients treated with trastuzumab deruxtecan. Distinct inflammatory and fibrotic signatures differentiated ILD cases from matched controls, with consistent associations observed between selected miRNAs and immunemediators. A subset of these alterations was also found in ILD cases attributed to everolimus or abemaciclib. These findings support the potential utility of circulating biomarkers in drug-induced ILD and may provide a basis for future studies focused on early detection and patient stratification.Elevated expression levelsin ILD cases compared tocontrols (UP)HSA-miR-aHSA-MIR-bHSA-MIR-cHSA-MIR-d+HSA-MIR-eHSA-MIR-fHSA-MIR-gHSA-MIR-hHSA-MIR-iHSA-MIR-jHSA-MIR-kHSA-MIR-lDecreased expressionlevels in ILD casescompared to controls(DOWN)HSA-miR-mHSA-miR-nHSA-miR-oHSA-miR-pHSA-miR-qTable 1 List of candidate mRNAs as biomarkers for ILD. Citation Format: M. Alva Bianchi, M. Cobos, R. Sánchez-Bayona, P. Tolosa, I. Diaz, L. Lema, A. Madariaga, J. Montes, W. Parra, C. Martín-Arriscado, M. Luis, L. Manso, M. Dueñas, E. Ciruelos Gil. Circulating microRNA and cytokine signatures associated with interstitial lung disease in patients treated with trastuzumab deruxtecan [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-09-26.