Protein gene product (PGP) 9.5 in diagnostic (neuro-) oncology. An immunomorphological study

Most likely identical to ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCH-L1), protein gene product (PGP) 9.5 is one of the major constituents of cytoplasmic polypeptides in neurons. The antigen seems to be expressed almost exclusively in neuronal and neuroendocrine tissues and their neoplasms. PGP 9.5 is also present in undifferentiated embryonic neoplasms like primitive neuroectodermal tumors (PNETs). However, the significance of PGP 9.5 as a marker in diagnostic (neuro-) oncology has not been systematically evaluated yet. In the present study the sensitivity and specificity of the widely used antiserum against PGP 9.5 has been retrospectively examined on 290 formalin-fixed, paraffin-embedded tumors of the nervous system and small round blue cell tumors. The presence of the antigen in tumors of neuronal (24/24) and neuroendocrine (63/73) differentiation confirm PGP 9.5 as a sensitive marker of these tumor groups, particularly in the diagnosis of pituitary adenomas where the expression was neither related to the staining behavior of the tumors in the PAS-orange G-reaction nor to their degree of polypeptide- and glycoprotein hormone activity. The nearly constant immunostaining of medulloblastomas (18/19) and other PNETs (5/6) demonstrate the role of PGP 9.5 as an additional marker in the detection of these embryonic tumors as this peptide was not or only weakly found in glial (11/58), meningeal (5/29), and nerve sheath neoplasms (1/28). On the other hand, the significance in the differential diagnosis of small round blue cell tumors seems to be limited because of positive immunoreactions in neuroblastomas (7/7) and oat cell carcinomas of the lung (7/7) although rhabdomyosarcomas (1/6) and malignant Non-Hodgkin-lymphomas (0/13) react completely negative in our series.