Innate immune reactions in locally limited tonsillar cancer

Tonsillar cancers often present as locally limited tumors but with cervical metastases. When the primary tumors of tonsillar cancers with cervical metastases are as small as clinically occult, the clinical features are diagnosed as primary-unknown cervical metastases. However, little is known as to why small tonsillar cancers establish cervical metastases. The aim of this study was to investigate a possibility that innate immune reactions might suppress the growth of tumors arising in the palatine tonsils, because the palatine tonsils contain various immune effector cells. Infiltration of natural killer (NK) cells and macrophages, which are major innate immune cells, in surgically removed tumors from patients with locally limited tonsillar cancers and tongue cancers was immunohistochemically studied by using anti-CD57 and anti-CD68 antibodies. Phagocytosis of the tumor cells by macrophages was also studied by dual immunofluorescence labeling. The number of infiltrating CD57+ NK cells and CD68+ macrophages was significantly increased in locally limited tonsillar cancers in comparison to normal tonsils and tongue cancers. The phagocytosis of tumor cells by CD68+ macrophages was observed significantly more frequently in tonsillar cancers than in tongue cancers. These results indicated that the innate immune reactions were more strongly induced in locally limited tonsillar cancers than in tongue cancers, and might therefore suppress the growth of primary tumors in palatine tonsils. The innate immune reactions against cancers in palatine tonsils were suggested to be one of the possible etiologies for the developing of primary-unknown cervical metastases.