Cellular pleomorphism in papillary tumors of the pineal region.

Papillary tumor of the pineal region (PTPR) is a recently recognized entity. We present the pathologic findings of two cases of PTPR as examples, and discuss the presence of cellular pleomorphism in these tumors. Patient 1 is a 48-year-old man with a pineal region mass. The tumor had unique biphasic patterns, papillary/pseudopapillary areas, and increased mitotic activity. Juxtaposed areas had marked pleomorphism, including nuclear enlargement, smudgy chromatin, nuclear pseudoinclusions, and cytoplasmic vacuolation. Mitoses were absent in these areas. Immunohistochemical staining revealed strong S100 expression. CAM 5.2 and CK18 were strongly positive in a patchy fashion. MIB1 labeling indices were high in classic PTPR regions but very low in pleomorphic areas. Patient 2 was a 35-year-old male with a pineal region tumor characterized by papillary architecture and overall cellular monotony, rare mitoses, and pleomorphism as a more isolated finding, with associated nuclear enlargement and crowding. S100 and CAM 5.2 labeling were present, and MIB1 labeling index was very low throughout the tumor. We discuss the pathologic and phenotypic features of PTPR. Variable pleomorphism may be present, reflected in size variation and nuclear hyperchromasia, but was not accompanied by increased proliferative activity in these cases, suggesting a degenerative phenomenon.