Discordant lymphoma: MALT lymphoma of the stomach and follicular lymphoma of the parotid gland

More than one histological type of malignant lymphoma can occur simultaneously in an individual. The entity is classified as either composite or discordant lymphoma. Both types of lymphoma, particularly discordant lymphoma comprised of extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue lymphoma (MALT-L) and follicular lymphoma (FL), are rare. We report a case of discordant lymphoma comprising MALT-L in the stomach and FL in the parotid gland. The patient was a 50-year-old Japanese woman who visited the University Hospital of Showa (Tokyo, Japan) because a barium study showed erosive gastric lesions. A gastro-intestinal endoscopy was performed 2 months after the barium study, which showed irregular erosions throughout the stomach body. A gastric biopsy showed MALT-L, and Helicobacter pylori (H. pylori) infection was confirmed. The patient had noticed a painless and elastic hard tumor mass of about 2 cm in diameter in the area of the left parotid gland 6 months before the barium study. We removed the parotid gland tumor and diagnosed it as FL 6 months after the barium study. We were able to diagnose the MALT-L and FL by morphological, immunohistochemical and molecular analyses of paraffin-embedded sections. This appears to be the first reported case of MALT-L and FL occurring together as a discordant lymphoma.