ALDH1 - A new immunohistochemical diagnostic marker for Schwann cell-derived tumors.

Although Schwann cell-derived tumors show typical histological features, the broad variety of spindle cell tumors that exist can impede the diagnostic procedure. In this study, we present aldehyde dehydrogenase 1 (ALDH1) as a new, viable diagnostic marker for Schwann cell tumors. Protein expression was examined by immunohistochemistry in schwannomas, neurofibromas, and malignant peripheral nerve sheath tumors (MPNST) as well as in non-neoplastic peripheral nerve sheath specimens. Meningiomas and other spindle cell-like tumors served as control tissue. ALDH1 immunohistochemistry was performed on human FFPE samples. Staining evaluation was performed according to a defined immunoreactive score. All schwannomas and neurofibromas were strongly positive for ALDH1. MPNST were positive too, but with a clear reduction of ALDH1 expression. All non-Schwann-cell-derived tumors showed no immunoreaction. This leads to the conclusion that ALDH1 can serve a as viable diagnostic marker for schwannomas and neurofibromas as it was expressed and detected by IHC in all samples. Furthermore, ALDH1 expression seems to be a sign for differentiation as it diminishes during malignization of Schwann cell tumors. Hence, its expression level provides information about the biological behavior of the tumor.