<p>Triggering receptor expressed on myeloid cells 2 (TREM2) has been shown to confer immunosuppressive effects when expressed on tumor associated macrophages and thus has become a prominent focus of cancer research in recent years. The primary aims of this study were to explore the distribution of TREM2-expressing macrophages in early-stage ER+ breast cancer, specifically asking if there is a correlation with tumor aggressiveness and/or metabolic syndrome. To address these aims, we performed immunofluorescent staining for TREM2, CD68, and DAPI in 95 early-stage breast cancer samples from patients who underwent surgery at Vanderbilt University Medical Center. We assessed associations between TREM2⁺CD68⁺ cell density in three distinct regions of the tumor and multiple tumor characteristics, prognostic factors, and metabolic syndrome criteria. Although some analyses, including associations with menopausal status, hormone receptor expression, and histological subtype, reached statistical significance, the overall data revealed no significant associations between TREM2-expressing macrophages and tumor prognostic factors or metabolic syndrome criteria in early-stage ER+ breast cancer. Consequently, our results indicate that TREM2 likely does not serve as a reliable biomarker for ER+ breast cancer. However, TREM2 may still hold prognostic value in other subtypes such as triple negative breast cancer.</p>