Cytokeratin 7 and 20 expression in choroid plexus tumors: Utility in differentiating these neoplasms from metastatic carcinomas

Tumors derived from choroid plexus epithelium are uncommon and may exhibit a wide variety of histologic patterns. They often are difficult to distingu ish from metastatic carcinomas. Previous studies that addressed this issue yielded conflicting results. Recent reports have demonstrated that evaluati on of coordinate expression of cytokeratin (CK) 7 and CK20 aids in distingu ishing primary from metastatic lesions in a number of anatomic sites and th at tumors that commonly are metastatic to the brain retain their CK7/CK20 i mmumophenotype in this location. We examined 35 choroid plexus tumors with a panel of antibodies to determine their CK7/CK20 immunophenotype. Tumors f rom 35 patients (7 male, 28 female; mean age, 25 years), including 31 choro id plexus papillomas and 4 atypical papillomas, were evaluated. All tumors were intraventricular or within the cerebellopontine angle and composed pre dominantly of orderly columnar epithelial cells resting on distinct fibrova scular cores. Atypical papillomas contained combinations of focal loss of a rchitectural pattern, increased mitotic activity, necrosis, and brain paren chymal invasion. No lesion was unequivocally malignant. Twenty-six tumors ( 74%), including all atypical papillomas, were CK7 positive and CK20 negativ e. Two tumors stained with both markers, one stained with CK20 only, and si x stained with neither marker. Other findings included expression of glial fibrillary acidic protein in 24 tumors, S-100 protein in 19 tumors, transth yretin in 31 tumors, Ber EP4 in 1 tumor, CAM5.2 in 33 tumors, epithelial me mbrane antigen in 4 tumors, and pancytokeratin in 27 tumors. Our results in dicate that the majority of choroid plexus tumors have a CK7-positive/CK20- negative immunophenotype. This finding may be useful in differentiating the se lesions from metastatic carcinomas that have differing CK7/CK20 profiles .