Malignant Cutaneous Peripheral Nerve Sheath Tumour with Rhabdomyosarcomatous Differentiation (Triton Tumour) in a Domestic Cat

A.L Stoll,A Suárez-Bonnet,B.A Summers,S.L Priestnall

doi:10.1016/j.jcpa.2018.09.003

Abstract

Divergent differentiation is encountered frequently within human malignant peripheral nerve sheath tumours (MPNSTs). The new component is often a rhabdomyosarcoma, but in animals this specific form of divergent differentiation within MPNSTs has only been reported once (in a dog). Incisional wedge biopsy of a locally extensive, ventral abdominal wall mass, which extended from the dermis to the subcutis, from a 12-year-old female domestic shorthaired cat, was performed. The tissue was examined with routine haematoxylin and eosin staining and immunohistochemical methods. A malignant neoplasm with spindle and polygonal cell components and progression towards a rhabdomyosarcomatous phenotype was observed. Both neoplastic cell populations exhibited strong expression of vimentin and there was multifocal expression of S100 and desmin. There was strong cytoplasmic labelling for α-sarcomeric actin and muscle actinand weak labelling for myoglobin within the cells positive for desmin. There was multifocal positive nuclear labelling for myogenin. Glial fibrillary acidic protein, α-smooth muscle actin, microphthalmia-associated transcription factor and melanoma antigen recognized by T cells were not expressed. Microscopical features, aided by immunohistochemistry, identified a MPNST with progression towards a rhabdomyosarcomatous phenotype, a so-called 'triton tumour'. A Schwann cell component could account for the divergent patterns of growth, given the plasticity of the neural crest. Nerve sheath tumours have been reported in the skin and subcutis of cats and are a differential diagnosis of feline cutaneous spindle cell neoplasms.

Highlights

The failure to label this malignant Peripheral nerve sheath tumours (PNSTs) is not surprising, as mentioned above and described by Schoniger et al Schwannomas and a variety of neurofibromas have been identified in several species (Schoniger and Summers, 2009; Schoniger et al, 2011) and probably occur in the cat
In the largest series of feline PNSTs published (Schulman et al, 2009), they were classified only as benign or malignant, some of the microscopical patterns of growth described (i.e. Antoni A, Antoni B, Verocay bodies) would imply that some were schwannomas. This cutaneous mass was interpreted as being a malignant PNST, and its mixed nature, evident in haematoxylin and eosin (HE)-stained sections, reflects a tumour containing undifferentiated neoplastic cells mixed with areas with progression towards a rhabdomyosarcomatous phenotype
Based on human experience with this entity, the interpretation is that both undifferentiated and differentiated components are derived from one PNS cell type, and S100 expression points to this being a Schwann cell

Summary

Introduction

Human MPNSTs may contain areas of ‘divergent differentiation’, the development of a second and different malignant lineage within the primary nerve sheath neoplasm, most often into a skeletal muscle sarcoma, but angiosarcomatous, chondrosarcomatous, osteosarcomatous and carcinomatous patterns are recognized (Ducatman and Scheithauer, 1984). Within the looser, more myxoid areas, strong cytoplasmic labelling with desmin was observed in single and multinucleated neoplastic cells, suggesting recapitulation of myogenesis (Fig. 4).

Results

Conclusion