Presence of lymphocyte membrane surface markers on "small cells" in a pineal germinoma

A 16-year-old boy was operated on via an occipital transtentorial craniotomy for a pineal tumor. Routine histological examination of the tissue revealed it to be a germinoma, as characterized by the presence of two cell populations: large cells and small, lymphoid-appearing cells. The cells were evaluated in a single-cell suspension for the presence of lymphocyte membrane surface markers; small cells exclusively were found to have such markers. A T-lymphocyte membrane marker was present in 51% of the small cells, whereas 15 to 18% of the small cells had a B-lymphocyte membrane marker.