Eosinophil Influence on Tumor and Stromal Responses in Breast Cancer Models

Eosinophils are components of the tumor microenvironment, but their role in breast cancer remains poorly understood and may depend on the cellular context. Here, we evaluated the effects of eosinophils in three-dimensional breast cancer models composed of murine 4T1 and 67NR or human MDA-MB-231 and MCF-7 breast cancer cells were cultured as homotypic spheroids or in heterotypic co-culture with NIH/3T3 or HFF fibroblasts. Murine bone marrow-derived eosinophils (BMEos) or human peripheral blood eosinophils were incorporated into the corresponding models. Spheroid growth was monitored for up to seven days, migration was assessed after mitomycin C treatment, IL-6 and IL-33 were quantified by ELISA, and PGD₂ and cysteinyl leukotrienes were measured by enzyme immunoassay. Eosinophils did not markedly alter spheroid growth under the evaluated conditions. In the murine models, however, BMEos appeared to modulate migration in a spheroid composition-dependent manner, with a trend toward reduced migration in homotypic tumor spheroids and increased migration in NIH/3T3 spheroids. BMEos also appeared to influence inflammatory mediator production, with IL-6 and PGD₂ levels tending to increase mainly in fibroblast-containing conditions, whereas IL-33 and cysLTs showed more modest or variable changes. Overall, these preliminary data suggest that eosinophil effects in breast cancer models depend on the tumor–stromal context and may be more evident in migration and inflammatory mediator production than in spheroid growth.