E-Cadherin–Negative Primary Small Cell Carcinoma of the Breast

Abstract

Primary small cell carcinoma of the breast is exceedingly rare, with fewer than 25 reported cases. The case presented herein is that of a 61-year-old woman with a 2.5-cm mass of the left breast. She underwent mastectomy with axillary node dissection. Histologic examination revealed sheets and nests of small, hyperchromatic, malignant cells with indistinct nucleoli and scant cytoplasm. High-grade solid and comedo ductal carcinoma in situ also was present. Two of 5 axillary lymph nodes contained metastatic disease. Immunohistochemical analysis demonstrated weak immunoreactivity for cytokeratin, neuron-specific enolase, and bcl-2. This histologic and immunohistochemical profile was consistent with that of a primary small cell carcinoma. Interestingly, this neoplasm lacked immunoreactivity for E-cadherin. E-cadherin expression has been documented in all 11 (100%) of 11 previously reported cases of primary small cell carcinoma of the breast, suggesting that this tumor is a form of ductal carcinoma. To our knowledge, this is the first reported case of E-cadherin-negative small cell carcinoma of the breast, which raises the question of a possible lobular histogenesis in some of these neoplasms.