Primary pulmonary primitive neuroectodermal tumor (PNET): A clinicopathological and immunohistochemical study of six cases

Background: The clinicopathological and immunohistochemical features of six primary pulmonary primitive neuroectodermal tumors (PNETs) are reported. Methods: The patients were four men and two women aged 22-56 years (mean = 32.3 years). The main presenting symptoms included chest pain, shortness of breath, and cough. The tumor size ranged from 4 to 9.6 cm. Results: Macroscopically, the tumors were circumscribed, yellow-white in color, and of soft and friable consistency. Histologically, the lesions were composed of a monomorphic population of solidly packed round cells with a round-to-ovoid nucleus, fine chromatin, small nucleoli, and scanty pale cytoplasm. Immunohistochemically, the tumor cells were uniformly positive for CD99, neuron-specific enolase, and vimentin, and single cases focally expressed cytokeratin and S100. Fluorescence in situ hybridization analysis performed in two cases showed positive rearrangement for the EWSR1 gene at the 22q12 locus. Follow-up information available for four patients showed that three had died 24-54 months after diagnosis and one patient is alive 11 months after diagnosis. Two patients were lost to follow-up. Conclusion: Primary PNETs of the lung are rare tumors that need to be added to the differential diagnosis of primary pulmonary neoplasms composed of small cells. Awareness of this entity as a primary pulmonary neoplasm is required in order to avoid misdiagnosis and unsuitable treatment of patients.