Spontaneous regression of a residual pineal tumor after resection of a cerebellar vermian germinoma.

A case of multiple intracranial germ cell tumor in which a pineal tumor regressed spontaneously after resection of the cerebellar mass is reported. Immunohistochemical staining of the cerebellar mass showed that most of the infiltrating lymphocytes were positive for CD3 and CD8. The anti-Ki-67 monoclonal antibody MIB-1 staining of the resected tumor revealed a high MIB-1 positivity ratio (36.1%) among the large tumor cells, and TUNEL staining demonstrated that positivity in up to 6% of the tumor cells. Possible mechanisms responsible for this spontaneous regression including immunological responses and apoptosis induced by T lymphocytes are discussed.