Assessment of Tissue Eosinophilic Infiltration in Invasive Mammary Carcinoma

Background: Stromal inflammatory cells in malignant tissue have recently gained increasing interest. Unlike the extensive research on tumor-infiltrating lymphocytes, published data about tumor-infiltrating eosinophils in breast cancer are scarce. Furthermore, similar studies have yet to be conducted in Iraq. Aims: The objective of this study is to examine the presence of eosinophilic infiltration by direct visualization using light microscopy and to analyze its relationship with other histological parameters in a group of Iraqi women diagnosed with invasive mammary cancer. Methods and material: A retrospective study enrolled 90 histological samples of invasive mammary carcinoma provided by core needle biopsy from a single center, together with their immunohistochemical results for ER and HER2-NEU. Data reviewing, direct morphological visualizations, and counting eosinophilic infiltration in tissue sections were done by two independent pathologists using light microscopy. The results were statistically correlated with the grade, ER, HER2-NEU, calcification, and axillary lymph node status at presentation. Results: Out of the entire sample size (90), 40 (44%) showed the presence of eosinophilic infiltration in the tissue, both intratumoral and stromal. Further analysis revealed that most eosinophilic infiltrates had an intermediate score (4-19) per 10 consecutive high-power fields. A strong and meaningful statistical relationship was seen between tissue eosinophilic infiltration and HER2/NEU status. A statistically insignificant correlation was seen between tissue eosinophilic infiltration and histological grade, ER receptor status, calcification, and axillary lymph node status at presentation. Conclusions: Eosinophils are tumor-infiltrating cells in breast cancer, both intratumoral and stromal. The presence of tissue eosinophilic infiltration can predict HER2/NEU negativity in breast cancer.