Malignant cells of epithelial phenotype limited to thoracic lymph nodes.

Asymptomatic thoracic lymphadenopathy was incidentally discovered in three patients with no definitive diagnoses. Enlarged lymph nodes, removed at thoracotomy, had irregularly distributed, pleomorphic, malignant-appearing cells. Mitoses were frequent. Electron microscopy showed tonofilament bundles and desmosomes. By immunocytochemistry, these cells uniformly expressed desmoplakin and cytokeratins 8 and 18 and various patterns of coexpression with other cytokeratins. One patient had lymphadenectomy, segmental lung resection and radiotherapy; the second had lymphadenectomy and later a lymphadenectomy with pneumonectomy; and the third had lymphadenectomy and radiotherapy. Neoplastic cells were detected exclusively within thoracic lymph nodes. The patients are well 111, 39 and 13 months after initial presentation. The clinical course and the patterns of intranodal distribution and marker expression of the neoplastic cells are unusual and distinct from most carcinomas metastatic to lymph nodes and reminiscent of "lymphoepithelioma-like carcinomas" described in the thymus and other sites. While the malignant cells may reflect metastases from as yet occult primaries or malignantly transformed ectopic epithelial nests, these tumours may arise by transformation from the cytokeratin-positive "extrafollicular reticulum cells" indigenous to lymphoid organs.