Small Glandular Proliferations of the Breast With Absent or Attenuated Myoepithelial Reactivity by Immunohistochemistry: A Review Focusing on the Differential Diagnosis and Interpretative Pitfalls

Abstract

Context.—Small glandular proliferations of the breast encompass a variety of benign, atypical, and malignant lesions that show some overlapping morphologic features. Myoepithelial stains are frequently used in the workup of these lesions in order to rule out or establish a diagnosis of invasive carcinoma. Some benign lesions show absent or diminished myoepithelial staining, and may represent an interpretative pitfall, particularly in small core biopsy samples. Objective.—To review small glandular proliferations of the breast that show absent or diminished staining with myoepithelial immunohistochemical markers. Data Sources.—The study comprised a review of published literature and clinical case material. Conclusions.—The interpretation of myoepithelial stains in small glandular proliferations of the breast can, on some occasions, represent a challenge in diagnosing these lesions. Recognition of the key histopathologic features and immunohistochemical staining patterns of the entities in the differential diagnosis is crucial in their workup.