Interleukin-6-producing thymic squamous cell carcinoma associated with Castleman's disease and nephrotic syndrome.

When a 63-year-old man was hospitalized with nephrotic syndrome due to focal segmental glomerulosclerosis, a mediastinal mass was discovered. A biopsy specimen obtained by mediastinoscopy showed findings compatible with the plasma cell type of Castleman's disease. Fever, anemia, and anti-nuclear antibody were present. Serum concentrations of gamma globulin, acute phase proteins, and, most strikingly, interleukin-6 (IL-6) were elevated. Methylprednisolone pulse therapy resulted in no clinical improvement. Pathologic examination of the resected thymic tumor showed a squamous cell carcinoma immunoreactive for IL-6. To our knowledge, this case represents the first reported IL-6-producing thymic squamous cell carcinoma associated with Castleman's disease and nephrotic syndrome.