[A rare case of nerve-sheath sarcoma with rhabdomyoblastic differentiation (malignant triton tumor)]

Abstract

Malignant peripheral nerve sheath tumors (MPNST) are spindle-cell sarcomas that appear in a setting of neurofibroma or schwannoma or are associated with peripheral nerves or demonstrate nerve sheath differentiation. Malignant triton tumor (MTT) is a subtype of MPNST that also contain tissue with skeletal muscle differentiation (embryonal, plemorphic and botryoid rhabdomyosarcoma). The estimated incidence of MPNSTs in patients with NF1 is 2-5% compared with 0.0001% in the general population and approximately 69% of the reported cases of MTT are associated with von Recklinghausen disease. In July 2002 a 37-year old man was readmitted to the Department of Oncologic Surgery of the S. Camillo-Forlanini Hospital in Rome for both a right-sided retroperitoneal paravertebral not palpable mass, incidentally detected at a follow-up MRI, and a left-sided popliteal mass, discovered at clinical evaluation. Seventeen months before, when the patient underwent surgery at the same Department for both a left-sided paravertebral inferior mediastinal neurofibroma and a right-sided axillary neurofibroma, diagnosis of von Recklinghausen disease (NF1) was made, according to the criteria established by the NIH Consensus Development. Conference on Neurofibromatosis of 1987. A xifopubic laparotomy was performed: the tumor appeared to be localized, well-capsulated and strictly associated to the lumbar and sacral nervous radicles (L4, L5, S1) without evidence of invasion. The tumor was completely resected with sparing of the psoas muscle and the lumbar plexus through a subperineural dissection technique. No intra-operative pathologic examination was performed. Postoperative pathologic findings showed evidence for a trition tumor. The popliteal mass was resected too and resulted to be a neurofibroma just like the tumors resected 17 months before when diagnosis of von Recklinghausen disease was made. The patient was disease free 6 months after initial surgery. Sarcoma arising in anatomic site other than extremity and superficial trunk are often more difficult to control because of anatomic constraints, delayed disease presentation, proximity to neurovascular and osseous structures and toxicity for normal adjacent tissues that limits the use of adequate radiation doses. Indeed, the anatomic site is an important prognostic factor in STS and the prognosis for retroperitoneal tumors is considerably worse than for extremity tumors. Reported local recurrence rates for retroperitoneal sarcomas range from 40% to 80% and, in marked contrast to extremity STS, most of patients can and do die from local recurrence in the absence of metastasis. In contrast to the benefit most patients with high grade soft tissue sarcomas of the extremities receive from adjuvant radiation and chemotherapy, these modalities have been of little value for retroperitoneal tumors. To overcome the problem of dose limitation, intraoperative electron beam radiotherapy (IORT) in combination with ERBT has been proposed. IORT plus ERBT was found to improve local control of disease in recent clinical trials. Current chemotherapy for retroperitoneal sarcomas is ineffective. Local adjuvant therapy such as intraperitoneal chemotherapy or experimental immunotherapy seems to be attractive in theory, but needs further investigations through prospective randomized multicentric trials. In conclusion, to date aggressive surgical management remains the most effective modality for selected primary and recurrent retroperitoneal soft tissue sarcomas including MPNSTs and the subtype MTT. Patients with incomplete resection and other risk factors such as younger age and high grade tumors may be suitable candidates for investigational adjuvant therapy.