Low-grade B-cell lymphoma of mucosa-associated lymphoid tissue in the thymus of a patient with pulmonary amyloid nodules

Low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT-type l ymphoma) is a rare thymic tumor, with only seven previous cases described w orldwide to date. We describe the only case to have presented with pulmonar y amyloid nodules. A 63-year-old Japanese female was found to have an anter ior mediastinal tumor and multiple bilateral pulmonary nodules during a med ical check-up in 1990 followed by chest radiography and computerized tomogr aphy, Because the mediastinal tumor grew larger, she was referred to the Na tional Cancer Center Hospital East and hyperglobulinemia was pointed out. T he thymus was resected through median sternotomy and pulmonary nodules were also resected through left thoracotomy. The solid and nodular tumor with s everal small satellite extensions and cyst formation was completely confine d to within the thymus and the resected pulmonary nodules consisted of soli d masses with a rough surface. Histologically, monotonous medium-sized cent rocyte-like cells occupied the medulla of the thymus and infiltrated Hassal l's corpuscles (lymphoepithelial lesions) and the resected pulmonary nodule s consisted of eosinophilic amorphous deposits which showed birefringence o n Congo Red staining. Immunohistochemically, the tumor cells were positive for CD20 and CD79a. IgG and kappa light chain restrictions were also found in plasmacytoid cells in the tumor. Clonal rearrangement of the immunoglobu lin heavy chain gene was demonstrated by polymerase chain reaction. We diag nosed this case as low-grade B-cell MALT-type lymphoma in the thymus and no dular pulmonary amyloidosis. Since the patient had only localized amyloid d eposits in the lung far from the thymic malignant lymphoma and had high ser um immunoglobulins, the pulmonary amyloid deposits might be derived from a circulating precursor associated with hyperglobulinemia.