Eleonora Nicolò

Purpose of review: Liquid biopsy (LB) is rapidly transforming the management of hormone receptor-positive/HER2-negative (HR+/HER2−) metastatic breast cancer (mBC). In this review, we discuss the most recent findings on circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs), exploring their roles across the treatment continuum, from treatment selection to resistance monitoring. Recent findings: ctDNA-based detection of actionable mutations – including ESR1 and PIK3CA – achieved regulatory validation as a primary predictive biomarker for treatment selection, supporting the approval of novel endocrine agents and targeted therapies in HR+/HER2− mBC. Serial ctDNA monitoring demonstrated the ability to intercept emerging resistance mechanisms ahead of radiological progression, opening a window for preemptive therapeutic adaptation. CTCs enumeration maintains robust independent prognostic value, with emerging evidence supporting its role in guiding treatment escalation and de-escalation decisions. Integrated multiparametric LB approaches combining CTCs and ctDNA are crucial to improve prognostic accuracy and clinical decision-making. Summary: LB is progressively shifting from a research tool to a clinical decision-making instrument in HR+/HER2− mBC. Prospective interventional trials, methodological standardization, and integrated strategies are needed to fully translate its potential into improved patient outcomes.

Inflammatory breast cancer (IBC) is a rare yet highly aggressive subtype of breast cancer, characterized by distinct clinical features, rapid progression, and complex biology. Despite decades of research, patient outcomes remain poor, underscoring the need for innovative approaches. The International IBC Symposium 2025 convened global experts to discuss advances in the field and to outline strategic priorities for research and clinical care. This report summarizes the key themes discussed. A major topic was IBC biology, with particular emphasis on tumor emboli formation and tumor microenvironment interactions, which shape the distinctive characteristics of the disease. Updates in molecular and immune profiling were presented, illustrating how these data may guide personalized therapeutic approaches. From a therapeutic standpoint, the importance of trimodal therapy in patients with nonmetastatic IBC was reinforced, while highlighting the need to investigate novel agents, rational drug combinations, and biologically informed strategies to improve outcomes. Additional sessions addressed optimization of locoregional management, even for selected patients with metastatic disease. Experts also discussed emerging technologies, including spatial transcriptomics, artificial intelligence tools, and liquid biopsy, as promising methods to advance disease characterization, facilitate earlier detection, and refine disease monitoring. Finally, a common theme across presentations was the critical importance of expanding awareness and education, as well as fostering global collaboration through the IBC International Consortium to standardize diagnosis, accelerate translational research, and ensure equitable access to care. Collectively, these efforts aim to redefine the clinical trajectory of IBC and move the field closer to achieving durable disease control and, ultimately, curative outcomes.

Metastasis is the leading cause of death in patients with breast cancer (BC), but the mechanisms underlying metastasis formation are still poorly understood. Circulating tumor cells (CTCs) are considered the main seed of metastasis with demonstrated prognostic impact in patients with BC. They are conventionally identified as cells positive for epithelial markers and lacking leukocyte markers. Nonetheless, circulating cells expressing both markers [dual-positive cells (DPcells)] have been reported but poorly investigated. Here, we evaluated, in a cohort of 340 patients with advanced BC, the prognostic impact of DPcells, showing their association with worse survival, particularly in patients with less than five CTCs. Their prognostic value varied among BC subtypes, with greater relevance observed in triple-negative and HER2-positive BC. Moreover, by performing single-cell genomic profiling of DPcells isolated from patients, we detected genomic aberrations in 28 and 93% of analyzed DPcells and CTCs, respectively. In vivo, DPcells were detected only in the blood of immunocompetent but not immunodeficient mice and no differences in the lung metastatic colonization ability of DPcells versus control cancer cells were observed. Our findings highlight the importance of studying this overlooked subpopulation of CTCs as a prognostic biomarker in BC, which might be particularly important in specific BC subtypes. Moreover, our results support the malignancy and metastasis-forming capability of DPcells and underline the need for future studies better defining the origin of these cells.

The advent of next-generation antibody-drug conjugates (ADCs), particularly trastuzumab deruxtecan (T-DXd), has transformed our understanding of human epidermal growth factor receptor 2 (HER2) targetability for breast cancer (BC) treatment. Historically categorized as HER2-positive or HER2-negative on the basis of trastuzumab eligibility, this classification has evolved significantly over the past 5 years. The DESTINY-Breast04 trial marked the entry of anti-HER2 therapies for patients with HER2-low BC, while DESTINY-Breast06 demonstrated the potential for earlier and broader use of T-DXd. The latter trial revealed that even minimal HER2 expression in tumors previously classified as HER2-0 might be clinically relevant and targetable with T-DXd. This has led to further refinement of HER2 classification, introducing the concepts of HER2-ultralow (HER2-0 with staining) and HER2-null BC (HER2-0 without staining). With these findings, most patients with metastatic BC are currently considered eligible for T-DXd. Accurately identifying candidates for these therapies has highlighted the limitations of current HER2 diagnostic practices, on the basis of immunohistochemistry (IHC)/in situ hybridization assessment. IHC assay, optimized to detect high levels of HER2 protein, faces limitations in discriminating finer variations at the lower end of the HER2 expression spectrum. This is further complicated by the heterogeneity of HER2 expression. To overcome these barriers, new approaches may be required. Quantitative methods for HER2 membrane assessment, genomic and transcriptomic evaluations of HER2, and the integration of artificial intelligence into tissue analysis hold promise and are currently under investigation. Additionally, noninvasive strategies, such as analysis of circulating tumor DNA or circulating tumor cells, may enable real-time HER2 status assessment and better patient selection for ADC. However, these techniques require rigorous validation to ensure their clinical utility. This evolving landscape underscores the need for improvement of diagnostic approaches to support the expanding role of ADCs in BC treatment.