Pathologic diagnosis of large cell neuroendocrine carcinoma of the lung in an axillary lymph node: a case report with immunohistochemical and molecular genetic studies.

The author herein reports a large cell neuroendocrine carcinoma (LCNEC) of the lung diagnosed in an axillary lymph node without clinical data, with an emphasis of KIT and PDGFRA. A 64-year-old woman presented with axillary and cervical lymph nodes swelling. An excisional biopsy of an axillary lymph node was performed under the clinical diagnosis of malignant lymphoma. The HE section showed a presence of large malignant cells arranged in a medullary pattern. The tumor cells had nucleoli. The HE diagnosis was large cell lymphoma or metastatic undifferentiated carcinoma, in particular large cell carcinoma of the lung. The tumor cells were positive for cytokeratins, p53 protein, thyroid transcriptional factor-1, neuron-specific enolase, synaptophysin, CD56, KIT, and PDGFRA. In contrast, they were negative for CD3, CD15, CD30, CD45, CD20, CD45RO, CEA, CA19-9, and chromogranin (Dako). Ki-67 labeling (Dako) was 100%. Therefore, a diagnosis of LCNEC of the lung was made. A molecular genetic analysis for KIT (exons 9, 11, 13, and 17) and PDGFRA (exons 12 and 18) identified no mutations. Later, a lung tumor and pleural effusion were detected, and the cytology of the effusion and sputum revealed carcinoma cells compatible with LCNEC. The patient was diagnosed as lung LCNEC, and treated by chemotherapy (cisplatin) and radiation (45 Gray). The present report is the first one with an examination of protein expression and gene mutations of KIT and PDGFRA in a metastatic focus of LCNEC of the lung.