Immunohistochemical Expression of Cd34 in Various Breast Lesions: A Narrative Review

Abstract

CD34 is widely employed in diagnostic breast pathology as an endothelial marker, but it is also expressed by a population of non-endothelial stromal fibroblastic cells, giving it dual diagnostic relevance. In breast lesions, CD34 immunohistochemistry provides complementary information by delineating vascular endothelium for assessment of angiogenesis and lymphovascular invasion, and by characterizing stromal fibroblasts in benign, preinvasive, and malignant conditions. This narrative review synthesizes validated evidence from published clinicopathologic, immunohistochemical, and outcome-based studies evaluating CD34 expression across the spectrum of breast lesions, including normal breast, benign proliferations, preinvasive disease, invasive carcinoma, spindle cell lesions, and vascular tumors. The literature consistently demonstrates that normal and many benign breast lesions show abundant CD34-positive, SMA-negative stromal fibroblasts, whereas invasive carcinoma is commonly associated with stromal CD34 loss and emergence of SMA-positive myofibroblasts, reflecting cancer-associated fibroblast activation. Importantly, similar stromal transitions may occur in ductal carcinoma in situ and benign sclerosing lesions, indicating that stromal CD34 loss is not specific for invasion. In invasive breast carcinoma, CD34-based microvessel density has been repeatedly associated with adverse outcomes, with meta-analytic evidence supporting its modest independent prognostic value, although methodological variability limits routine clinical adoption. CD34 also plays a supportive role in the differential diagnosis of spindle cell and vascular lesions, where its interpretation must be integrated with morphology and lineage-specific markers. In conclusion, CD34 is a versatile but context-dependent immunomarker in breast pathology, best utilized as part of a targeted immunohistochemical panel rather than as a stand-alone diagnostic or prognostic tool.