Peripheral nerve sheath tumors in goldfish (Carassius auratus) similar to human atypical neurofibroma

Cutaneous spindle cell tumors (SCTs) frequently occur in fishes, with peripheral nerve sheath tumors (PNSTs) being the most commonly reported neoplasms in goldfish. However, distinguishing PNSTs from other SCTs is not always possible relying only on routine cytological and histopathological findings. The aim of this study was to characterize 6 skin nodules of 6 cohabiting goldfish (Carassius auratus) resembling atypical neurofibromas in humans. Materials and methods Skin nodules were characterized using cytology, histopathology, histochemistry, and immunohistochemistry (IHC). Results Cytology and histopathology showed a SCT with nuclear atypia in all cases. Gomori’s reticulin stains revealed the presence of intratumoral basement membrane fragments. IHC displayed multifocal expression of the S100 protein and CNPase by tumor cells, intermingled with neurofilament-positive axons. Conclusion Collectively, these findings were consistent with a PNST resembling atypical neurofibroma in humans, an entity not previously reported in goldfish. The present findings suggested that reticulin stain, and IHC for S100 protein and CNPase are useful for identification of PNSTs in this species.