The rare case of synchronous bilateral breast metastasis from a lung neuroendocrine tumor (small cell lung carcinoma): a case report and literature review

Breast metastasis from small cell neuroendocrine carcinoma (SNEC) is very rare. In the present report, we describe a case of a female patient who was initially diagnosed with triple negative primary bilateral breast cancer, but during systemic examination, the diagnosis was bilateral breast metastasis from SNEC. A 62-year-old woman with no history of smoking presented to the Department of General Medicine with left-sided chest pain, and computed tomography revealed masses in both breasts and left pleural thickening that was further confirmed by mammography and ultrasound of the breasts. A needle biopsy was performed, and triple negative primary bilateral breast cancer was diagnosed. Because progastrin-releasing peptide (ProGRP) 37,300 pg/ml (normal range, 0–81.0 pg/ml) and neuron-specific enolase 35.0 ng/ml (normal range, 0–16.3 ng/ml) levels were elevated, thoracoscopic biopsy was performed, and SNEC was diagnosed. Pathological examinations showed that the bilateral breast masses were also positive for immunohistochemical staining of chromogranin A, synaptophysin, and CD56, leading to a diagnosis of bilateral breast metastasis of neuroendocrine tumor. Although very rare, the possibility of breast metastasis should be considered when malignancy is suspected in other organs.