Reactive lymphoid hyperplasia （RLH） is pathologically lymphoid hyperplasia and requires differentiation from malignant lymphoma. Development of RLH in the oral cavity is rare, and concomitant development with oral carcinoma has not previously been reported. We report two cases of RLH that developed with oral carcinoma. An 81-year-old Japanese woman with an upper gingival mass and a 72-year-old Japanese woman with a right tongue mass visited the Department of Oral and Maxillofacial Surgery, Gunma University Hospital. The masses were diagnosed as squamous cell carcinoma on biopsy, and RLH was found in the subepithelium adjacent to the carcinoma. RLHs included formation of a lymphoid follicle with germinal centers. No atypical lymphocytes were present in the germinal centers, most lymphocytes were CD20-positive, many tingible-body macrophages were observed, and Bcl-2 was negative. In addition, most lymphocytes were MIB-1-positive. RLHs were completely resected by biopsies. The cause of RLH development has not been determined. However, the cause of RLH development in the two patients described in this paper may have been due to a local hyperimmune reaction and induced by potentialization of cancer immunity and severe inflammation.
