The use of immunomorphology to differentiate choroid plexus tumors from metastatic carcinomas

The histologic and immunohistologic differential diagnosis of choroid plexus papillomas/plexus carcinomas (PP/PC) versus metastatic carcinoma in the brain is problematic.

Thirty-four choroid PP/PC from 28 patients, 5 normal choroid plexus, and 45 cerebral metastatic carcinomas were immunohistochemically examined with the monoclonal anti-epithelial noncytokeratin antibodies HEA 125 and Ber EP4 using the alkaline phosphatase anti-alkaline phosphatase (APAAP) method.

Normal choroid plexus epithelium was consistently negative. Sections from PP/PC of 3 of 28 patients demonstrated immunoreactivity for these antibodies. In contrast, 43 of 45 cerebral metastatic carcinomas displayed positive immunostaining for HEA 125, and 44 of these 45 carcinomas were positive for Ber EP4. Thus, sensitivity was higher for these antibodies than for the monoclonal anticytokeratin antibody KL1 (41/45). All three HEA 125/Ber EP4-positive PP/PC contained periodic acid-Schiff (PAS)-positive, tall columnar tumor cells. The intensively HEA 125, Ber EP4, and PAS-positive PP/PC were interpreted as possible transitional forms of the mucus-secreting and acinar PP/PC:

Despite this restriction, the authors proposed the application of HEA 125 and Ber EP4 as a reliable tool in the differential diagnosis of PP/PC versus metastatic carcinoma, especially in combination with glial fibrillary acid protein and transthyretin. Currently, all HEA 125/Ber EP4-positive PP/PC in patients older than 20 years proved to be metastatic carcinomas during their clinical course.