[P-24] Malignant triton tumour: case report

Henny S. Rejeki and Bethy S. Hernowo

Department of Pathological Anatomi, Faculty of Medicine, Universitas Padjadjaran, Bandung, Indonesia

Background: Malignant triton tumour (MTT) is a rare neoplasm, approximately 170 cases have been reported. Diagnosis of this tumour requires attention to the clinical, histopathological, immunohistochemical and prognosis features of this neoplasm.

Case Presentation: A 39-year-old male presented with a large mass in left neck gradually increasing in size. At one and twelve year (s) old, he underwent operation of a nodule in the same area. He had a relapse in 2014, initially as big as a chicken egg. In the last 1 year, it was getting bigger thus he complained of difficulty swallowing, eating and breathing. Previous biopsy diagnosed with neurofibroma. The resected mass consisted of a large globular mass, measuring 16 x 11 x 7 cm. Microscopic features showed alternate hypocellular and hypercellular areas composed of spindle cells with wavy nucleus, pattern of vascular growth with a haemangiopericytoma-like appearance, mitotic figures > 10/10 HPFs with abnormal mitoses, scattered large cells both rounded and elongated with abundant deep eosinophilic cytoplasm. The spindle cells showed focal positivity for S-100 protein. Desmin was stained in rhabdomyoblastic cells.

Discussion and Conclusion: MTT is a malignant peripheral nerve sheath tumour with skeletal muscle differentiation. The proposed classification of MTT is comprised of three following criteria, i.e. (a) it is related to peripheral nerve or occurs in patient with NF-1; (b) most of the tumour consist of Schwann cells; and (c) tumour contains rhabdomyoblasts. The tumour in this case also showed marbled appearance (alternating hypocellular and hypercellular areas) and contained heterologous differentiation (rhabdomyosarcomatous), brisk mitotic, focal positivity for S-100 and desmin. Tumor develops after a long period (10 – 20 years). Differential diagnosis is neurofibroma, but it can be ruled out by immunohistochemical S-100 (focal positivity). MTT is more aggressive than MPNST and is important as differential diagnosis.