Apocrine Breast Carcinoma With an Atypical Immunohistochemical Profile: A Case Report

Breast cancer is the most common malignancy among women worldwide and encompasses a wide variety of histopathological subtypes. While invasive ductal carcinoma (IDC) represents the most prevalent form, rare variants such as apocrine carcinoma (AC) also warrant particular attention. Classically, AC of the breast is defined by apocrine morphology, negativity for hormonal receptors (estrogen receptor (ER), progesterone receptor (PR)), and strong positivity for the androgen receptor (AR). However, the present case involving a 37-year-old woman who detected a nodule at the junction of the lower quadrants of the right breast illustrates an atypical variant of this tumor subtype. Histological examination revealed two lesions displaying typical apocrine carcinomatous proliferation but with an unusual immunohistochemical profile: ER expression at 80%, PR expression at 5%, and human epidermal growth factor receptor 2 (HER2) overexpression. This deviation from the classical apocrine profile highlights the biological heterogeneity of these tumors and underscores the importance of thorough characterization to optimize therapeutic management.