Next generation sequencing can be helpful in histologic diagnosis: A case report of metastatic breast cancer mimicking atypical carcinoid tumor of lung

Development of molecular technology has led to the expansion of next generation sequencing (NGS) in area of diagnostic pathology. Here we present a case in which a lung tumor, which resembled an atypical carcinoid tumor, was revealed as metastatic breast cancer by next generation sequencing. A 50-year-old female, who had received modified radical mastectomy for breast cancer, presented with a 2.1 cm sized lung mass. The mass was well-defined, well-enhanced, and showed endobronchial component by computed tomography. Under the impression of carcinoid tumor, right upper lobectomy was performed. Tumor cells were immunohistochemically positive for chromogranin and CD56, but negative for cytokeratin 7 and GCDFP-15. Initially, the patient was diagnosed with atypical carcinoid tumor. However, subsequent NGS test revealed GATA3 mutation (p.Ala333fs) of the lung tumor. After a thorough review of literature and public cancer genome data about GATA3 mutation, the diagnosis was revised to metastatic invasive carcinoma from breast.