Peripheral nerve sheath tumors (PNSTs) encompass entities with different cellular differentiation and degrees of malignancy. Spatial heterogeneity complicates the diagnosis and grading of PNSTs in some cases. In malignant PNST (MPNST) for example, single-cell sequencing data has shown dissimilar differentiation states of tumor cells. Here, we aimed to determine the spatial and biological heterogeneity of PNSTs. We performed spatial transcriptomics on formalin-fixed paraffin-embedded diseased peripheral nerve tissue. We used spatial clustering and weighted correlation network analysis to construct niche-similarity networks and gene expression modules. We determined differential expression in primary pathologies, analyzed pathways to investigate the biological significance of identified meta-signatures, integrated the transcriptional data with histological features and existing single-cell data, and validated expression data by immunohistochemistry. We identified distinct transcriptional signatures differentiating PNSTs. Immune cell infiltration, APOD, and perineurial fibroblast marker expression highlighted the neurofibroma component of hybrid PNSTs (HPNSTs). While APOD was evenly expressed in neurofibromatous tumor tissue in both, HPNST and pure neurofibromas, perineurial fibroblast markers were evenly expressed in HPNST, but restricted to the periphery in plexiform neurofibromas. Furthermore, we provide a spatial cellular differentiation map for MPNST, locating Schwann cell precursor and neural crest-like cells as well as those with mesenchymal transition. This pilot study shows that applying spatial transcriptomics to PNSTs provides important insight into their biology. It helps establish new markers and provides spatial information about the cellular composition and distribution of cellular differentiation states. By integrating morphological and high-dimensional molecular data it can improve PNSTs classification in the future.

Epithelioid malignant peripheral nerve sheath tumor (MPNST) is a rare subtype of MPNST composed of epithelioid cells with abundant cytoplasm. Currently, strong and diffuse immunostaining for S100 protein and SOX10 is generally regarded as a characteristic feature of epithelioid MPNST. However, malignant tumors with epithelioid morphology that arise from a peripheral nerve or a pre-existing benign nerve sheath tumor should be regarded as epithelioid MPNSTs when they do not show characteristic features that definitively lead to other specific diagnoses. Here, we describe 3 cases of epithelioid MPNST in the peripheral nerve or schwannoma that was negative for S100 protein and SOX10 expression. Instead, these tumors were positive for EMA, GLUT1, claudin 1, and cytokeratin to varying degrees, while all of them retained SMARCB1 and H3K27me3 by immunohistochemistry. EMA, GLUT1, and claudin 1 are known markers of perineurial cell differentiation; thus, they could possibly represent epithelioid MPNST with perineurial cell differentiation.

Malignant perineurioma is a rare subset of malignant peripheral nerve sheath tumors (MPNSTs) with ultrastructural and immunohistochemical features of perineurial differentiation, distinguishing it from other MPNSTs, which typically demonstrate Schwannian features. The clinical course and prognosis of this rare tumor is not well defined. The electronic medical records were searched for patients with a diagnosis of MPNST. Patients with a pathologic diagnosis of malignant perineurioma or MPNST with perineurial features were identified and further evaluated. Five patients with malignant perineurioma, or MPNST with perineurial features, were identified. Four patients (2 male and 2 female) were included with tumors associated with a common digital nerve, small muscular branch to the deltoid, sciatic nerve, and accessory nerve. One patient with the pathology diagnosis meeting inclusion criteria was excluded, as no clinical information was available for this patient. Patients in our series presented at varied stages of disease. Clinical courses after diagnosis of malignant perineurioma, where follow-up was available, were largely uncomplicated with regard to recurrence and metastatic disease. Careful follow-up is indicated, and further work is needed to characterize the clinical course of these rare tumors.

In 1938, the Malignant Triton Tumor (MTT) was first explained by Mason. Case 1: A man aged 28 years presented with chest pain and difficulty in breathing since last five months, there was no history of cough fever or night sweats. Clinical examination was unremarkable. His routine hematological tests including tumor markers were within normal range, testicular ultrasound was normal. CT scan of thorax revealed a mass in the anterior mediastinum. CT guided biopsy revealed a malignant triton tumor. Case 2: A 30 years old man, nonsmoker presented with history of chest tightness and feeling pressure while kneeling down since last 3 months, otherwise fit and healthy. His routine hematological investigations including tumor markers were within normal range. A CT scan of thorax revealed a large mass in the right posterior mediastinum. CT guided biopsy showed malignant triton tumor. Case 3: A man aged 28 years presented with chest pain and difficulty in breathing since last five months, there was no history of cough fever or night sweats. Clinical examination was unremarkable. His routine hematological tests including tumor markers were within normal range, testicular ultrasound was normal. CT scan of thorax revealed a mass in the anterior mediastinum. CT guided biopsy revealed a malignant triton tumor. Malignant peripheral nerve sheath tumors (MPNST) are uncommon sarcomatous tumors that are believed to be derived from Schwann cell or neighboring cells with perineurial differentiation. MTT is rarely reported in mediastinum, lung and heart (<10%) To the best of our knowledge, only few cases of MTT in the mediastinum have been reported in English literature, including, four were reported in the anterior mediastinum, three in the posterior mediastinum, one in the middle mediastinum and one between the ascending aorta and the main pulmonary artery. Most of the patients were young adults. We report three cases of rare mediastinal malignant triton tumors. They have been treated with palliative surgery/radical surgery +/- adjuvant therapy. The prognosis varied from a 3 month overall survival time to being alive at a 53 month follow-up period. In conclusion we report three rare cases of mediastinal malignant triton tumor treated with radical surgical resection and post-operative radiotherapy, one patient developed lung metastasis, and two had late local recurrence. The malignant triton tumor is a lethal neoplasm which carries very poor prognosis particularly when they occur in the mediastinum because it's very difficult to obtain wider tumor free margin due to the nature of location site.

Malignant peripheral nerve sheath tumour (MPNST) with perineurial differentiation is a rare variant of MPNST. The pathological features and clinical significance of this variant remain to be characterised. We reported the clinicoradiological and pathological features of a case of recurrent right arm mass related to the ulnar nerve in a 42-year-old female patient. On pathological examination, the tumour showed dual features of conventional and perineurial MPNST which was proven by positive immunostaining for S-100 and EMA. The pathological diagnosis was MPNST with perineurial differentiation. In addition, a peculiar and rare finding of intracytoplasmic eosinophilic hyaline globules (thanatosomes) within tumour cells is reported. We document a rare tumour with hybrid features between conventional and perineurial MPNSTs. Further studies are needed to establish its biological behaviour.