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

Although Schwann cellderived 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 celllike 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.