malignant peripheral nerve sheath tumor ( mpnst ) accounts for about 5 - 10% of all soft tissue sarcomas .
the fact that the presence of this tumor in the buttock region is extremely rare has prompted the authors to report this case .
this is an interesting tumor not encountered very much in the neuro - oncology literature .
it can occur in sporadic form or over a setting of neurofibromatosis-1 ( nf-1 ) .
when mtt develops over nf-1 , the diagnosis can be confirmed based on morphologic grounds supported by an immunostain such as s-100 protein .
a 40-year - old male presented with a large mass in the gluteal region gradually increasing in size over 6 months .
ten years back , operation of a nodule in the same area had revealed histopathological diagnosis of neurofibroma . on further questioning ,
the patient revealed having two small painful nodules over his back since the presence of the operated nodule .
his family history suggested that his father was a diagnosed case of von recklinghausen disease ( nf-1 ) .
the resected mass consisted of a large globular mass measuring 10  7  6 cm . the cut section showed solid grey - white and hemorrhagic areas ( fig .
1 ) . multiple sections studied revealed alternate hypocellular and hypercellular areas composed of spindle cells with wavy nucleus and nuclear palisading .
thick - walled blood vessels were seen with perivascular accentuation of tumor cells in the hypocellular areas ( fig .
mitotic figures were brisk in the cellular areas , 11/10 high power fields with few abnormal mitoses .
the tumor also showed a good number of scattered large cells both rounded and elongated with abundant deep eosinophilic cytoplasm and clearly visible cross striations ( fig .
the patient was subjected to radiotherapy on being referred to the oncology department . during a follow - up period of 8 months ,
slightly more than half of the cases of mtt have been reported in conjunction with nf-1 . in our case ,
when it occurs in sporadic form , other spindle cell sarcomas like fibrosarcoma , malignant fibrous histiocytoma and rhabdomyosarcoma can come as differential diagnosis .
the tumor develops after a long latent period of 10 - 20 years . in our case
there is an agreement that the diagnosis of mpnst can be on morphologic grounds supported by positivity for s-100 protein .
the morphologic features are ( a ) alternating hypocellular and hypercellular regions , ( b ) the appearance of thin wavy comma - shaped / bullet - shaped nucleus in the hypocellular areas , ( c ) presence of nuclear palisading , ( d ) presence of nerve whorls or tactoid bodies resembling wagner - meissner corpuscles , ( e ) prominent thick - walled vasculature , and ( f ) presence of heterologous elements like rhabdomyoblasts , cartilage and bone .
such tumors show focal positivity for s-100 protein in 50 - 90% of cases , suggesting a nerve sheath origin .
. the 5-year survival rate of mtts is only 5 - 15% in contrast to mpnsts where it is 50 - 60% .
integrated positron emission tomography and computed tomography have been used to assess remission and response to therapy .
the prognosis of mtt depends on the location , grade and completeness of surgical margins .
it is good for the head , neck , extremities and worse for other sites including the buttock . in a study
it was observed that mtt in association with nf-1 has a poor prognosis compared to sporadic forms .
 malignant peripheral nerve sheath tumor with rhabdomyoblastic differentiation , malignant triton tumor , has a rare incidence . 
 we report such a case in a 40-year - old male who presented with a mass over the buttock . 
 he was a previously diagnosed case of neurofibroma in the same area . 
 histomorphology supported by immunostaining with s-100 protein confirmed the diagnosis . 
 malignant triton tumor has a poor prognosis owing to its aggressive biological behavior . 
 the fact that the presence of this tumor in the buttock region is extremely rare has prompted the authors to report this case . 
Introduction
Case Report
Discussion