Metastatic non-small cell lung carcinoma a mimic of primary breast carcinoma—case series and literature review

Metastatic tumors to the breast are rare but constitute a major diagnostic dilemma. Of these, non-mammary carcinomatous metastases to the breast are particularly challenging and, without a clinical history, may be extremely difficult to distinguish from primary breast carcinoma (PBC). We specifically studied metastatic tumors of pulmonary origin, as the lung is one of the major primary sites for carcinomatous metastasis to breast. Sixteen metastatic lung tumors to the breast were identified in our archives between 1996 and 2017 including 12 non-small cell lung carcinomas (NSCLC), one large-cell neuroendocrine, one atypical carcinoid, and two small-cell carcinomas. Adenocarcinoma was the most frequent amongst the NSCLCs (11/14). We retrieved the clinical information of these cases and reviewed the pathological characteristics to provide practical tools for pathologists to aid in their identification. Even in the absence of a clinical history of lung cancer, metastatic pulmonary adenocarcinoma to the breast should be considered in at least one of the following scenarios: (1) single or multiple well-circumscribed lesions of the breast that lack an in situ component and that are accompanied by distant metastases but negative axillary lymph nodes, (2) breast tumors that are triple negative yet not high-grade, or (3) breast tumors presenting as stage 4 disease and/or having an unusually aggressive clinical course on standard breast therapy. Accurate and timely diagnosis of these tumors is mandatory because of treatment and prognostic implications.