Primary Mammary-Like Carcinoma of the Lung: A Case Report of a Distinct Type of Primary Lung Carcinoma.

A case of a primary lung carcinoma with histologic and immunohistochemical features of a mammary carcinoma is presented. The patient is a 72-year-old man who presented with symptoms of cough and dyspnea. Diagnostic imaging showed a bronchial tumor in the left lower lobe that was surgically resected by a left lower lobectomy. The tumor was characterized by a homogenous cellular proliferation composed of small to medium-sized cells with round nuclei and inconspicuous nucleoli. Multiple immunohistochemical stains were performed, and the tumor was notably positive for estrogen receptor, progesterone receptor, GATA3, and pan-keratin, while molecular analysis showed somatic mutation in ARID1A. Clinical follow-up showed that the patient is alive and well 18 months post-surgical resection without evidence of recurrence or metastatic disease. Based on the overall features of this neoplasm, we consider that the tumor herein presented represents an unusual type of lung carcinoma that we refer to as primary mammary-like carcinoma of the lung.