Eosinophils and cancer: Unexpected allies?

Long regarded as cells involved primarily in allergic responses and antiparasitic defence, eosinophils are now drawing increasing attention in oncology. A review article led by Marie Gilon, an oncology resident physician and PhD candidate at the University of Liège, synthesises current knowledge on how these white blood cells interact with tumour biology and may inform the clinical management of cancer patients.

Published in a peer-reviewed journal, the review draws on epidemiological and experimental data to map the multifaceted behaviour of eosinophils across different cancer types. Analyses of population-level studies suggest that higher eosinophil counts may be associated with a reduced risk of developing certain cancers. Once disease is established, however, the relationship between eosinophils and clinical outcomes proves more nuanced: their effect varies considerably depending on the tumour type and the biological context in which they operate.

At the cellular level, eosinophils can act directly against tumour cells through the release of cytotoxic proteins stored in their granules. Their influence extends beyond direct cytotoxicity, however: eosinophils also modulate the broader immune response by interacting with other immune cells, including lymphocytes. This capacity to shape the tumour microenvironment helps explain the sometimes contradictory findings observed in the literature, where the same cell type appears to both restrict and, in certain conditions, support tumour progression.

One area that has attracted particular interest is the relationship between eosinophils and immunotherapy. Several studies reviewed in the article indicate that elevated eosinophil counts, measured either before or during treatment with immune checkpoint inhibitors, are associated with improved treatment responses and longer patient survival. At the same time, the authors note that this immune activation is correlated with a higher incidence of immune-related adverse effects, underscoring the importance of careful patient monitoring. These findings suggest that eosinophil measurement could eventually serve as a practical tool to help clinicians identify patients most likely to benefit from immunotherapy and to anticipate potential complications.

The review was co-authored by Christine Gennigens, Claire Josse, Vincent Bours, and Guy Jerusalem, reflecting the collaborative effort between the Oncology Department of the CHU de Liège and the Human Genetics Unit at GIGA. This interdisciplinary approach, connecting laboratory findings with clinical observations, is central to the translation of basic research into diagnostic or therapeutic tools.

The authors are careful to acknowledge the limitations that still constrain the field. The variability of eosinophil behaviour across tumour types, combined with the absence of standardised measurement protocols, makes it difficult to draw uniform conclusions or establish clear clinical guidelines. Further research is needed to clarify the underlying mechanisms and to determine the conditions under which eosinophils might be reliably used either as biomarkers or as therapeutic targets.

This review positions eosinophils as cells worthy of sustained attention at the intersection of immunology and oncology. While considerable work remains before their clinical potential can be fully realised, the evidence reviewed by Gilon and colleagues points to a meaningful role for these cells in the evolving landscape of cancer immunotherapy.