Journal of Cytology

: 2019  |  Volume : 36  |  Issue : 4  |  Page : 213--214

Malignant triton tumor diagnosed on fine needle aspiration cytology

Biswajit Dey, Adarsh Barwad, Neelaiah Siddaraju, Pampa Ch Toi 
 Department of Pathology, Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), Puducherry, India

Correspondence Address:
Dr. Adarsh Barwad
Department of Pathology, Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), Dhanvantari Nagar, Puducherry - 605 006

How to cite this article:
Dey B, Barwad A, Siddaraju N, Toi PC. Malignant triton tumor diagnosed on fine needle aspiration cytology.J Cytol 2019;36:213-214

How to cite this URL:
Dey B, Barwad A, Siddaraju N, Toi PC. Malignant triton tumor diagnosed on fine needle aspiration cytology. J Cytol [serial online] 2019 [cited 2020 Jul 7 ];36:213-214
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Full Text

Malignant triton tumor (MTT) is a rare aggressive subtype of malignant peripheral nerve sheath tumor (MPNST) characterized by rhabdomyoblastic differentiation.[1] MTT generally arises from a peripheral nerve in the head, neck, extremities, or trunk. Rare sites include the brain, buttock, viscera, mediastinum, and retroperitoneum.[1] First described in 1932 by Masson and later named by Woodruff et al. in 1973, histopathological features of MTT have been adequately described in the literature.[2],[3],[4] However, there are only few case reports describing the cytological features of MTT.[5],[6] We report a case of MTT in a 42-year-old male diagnosed on fine needle aspiration cytology (FNAC).

A 42-year-old male presented with a mass in the left lower alveolus. It was progressively increasing in size. The patient gave history of wide local excision of a mass in the same site 1 year back followed by chemotherapy. This initial excision histology was diagnosed as MPNST. He was asymptomatic for 5 months. But then he had a recurrent mass in the site of surgery. On local examination, there was a globular mass measuring 5 × 4 cm in the left lower alveolus extending from the left first premolar to first molar. It was obliterating the left lower gingivobuccal sulcus.

Contrast-enhanced computed tomography showed a heterogeneously enhancing mass measuring 5.5 × 5 × 5 cm in the left lower gingivobuccal sulcus and the adjacent buccal mucosa. The body of the mandible was also involved. The left level IB, II, III, and IV cervical lymph nodes were enlarged. FNAC was performed. Smears were stained for May–Grunwald Giemsa and Papanicolaou (Pap) stains. Smears were richly cellular and showed two types of cells. The predominant cell types were the medium-sized polygonal to spindly cells arranged in pseudopapillaroid clusters and lying singly. These cells had oval nuclei with some having elongated nuclei with smooth contours and inconsistently tapered end. In some cells, nuclei had comma-shaped morphology [Figure 1]a. All these cells had finely granular, evenly dispersed nuclear chromatin. The other type of cells was large pleomorphic cells mostly clinging to the pseudopapillaroid clusters and lying discretely [Figure 1]a. These cells were oval to pear shaped with eccentrically placed nuclei and moderate to abundant cytoplasm [Figure 1]b.{Figure 1}

Subsequently, immunocytochemistry was performed on the Pap-stained smears without destaining with a panel of S100, desmin, MyoD1, myogenin, cytokeratin, smooth muscle actin, and HMB45. S100 showed both nuclear and cytoplasmic positivity in the medium-sized polygonal to spindly cells focally [Figure 1]c. Desmin showed cytoplasmic positivity in large pleomorphic cells. MyoD1 and myogenin showed nuclear positivity in those large cells [Figure 1]d. Cytokeratin, smooth muscle actin, and HMB45 were negative. A diagnosis of MTT was offered.

On the basis of cytological diagnosis, the patient underwent wide local excision of the tumor with left hemimandibulectomy and modified radical neck resection [Figure 1]e. On histopathological examination, the tumor was composed of spindle cells with good number of pleomorphic cells having eosinophilic cytoplasm [Figure 1]f. Some of these cells showed cross striations. Mitosis was brisk with 10/10 high-power field. Thus, the diagnosis of MTT was confirmed. The lymph nodes were free.

Postoperatively, the patient received adjuvant radiotherapy. However, the patient presented with an enlarged left cervical lymph node measuring 4 × 3 cm after 6 months of surgery. FNAC from the lymph node showed similar cytomorphology and a diagnosis of MTT was made.

MTT is a rare tumor, which constitutes 5% of all MPNSTs.[1] Most cases are reported in adults with a mean age of about 30 years.[1] However, patients of all ages have been described. MTT can occur in sporadic form or over a setting of neurofibromatosis-1 (NF-1).[1] It is estimated that between 40% and 70% of cases occur in patients with NF-1, with an earlier age of onset and predominantly in male subjects.[1] The sporadic cases are seen in females of older age group.[1]

Cytologically, MTT consists of a mixture of two types of tumor cells – the predominant oval to spindle cells and the other large pleomorphic cells.[5],[6] In the present case, the mixture of two tumor cells' population with immunocytochemical features clinched the diagnosis. Immunohistochemically, MTT shows positivity with S100 and Leu-7.[4] The rhabdomyoblastic differentiation is confirmed with positive staining with desmin, myoD1, and myogenin.[4] The important differential diagnoses of MTT are synovial sarcoma, leiomyosarcoma, fibrosarcoma, malignant melanoma, and pleomorphic rhabdomyosarcoma depending on the predominant cell type.[4] Therefore, immunostains are important to confirm the diagnosis. In the present case, cytomorphology along with S100, desmin, MyoD1, and myogenin positivity and cytokeratin, smooth muscle actin, and HMB45 negativity confirmed the diagnosis of MTT.

There are different hypotheses regarding the histogenesis of MTT. The most widely accepted one is the metaplastic theory, which states that malignant Schwann cells transform directly into striated muscle cells.[2],[4] Chemotherapy may induce rhabdomyoblastic differentiation in sarcomas including MPNST due to tumor differentiation. In the present case, the pathogenesis could be attributed to chemotherapy-induced rhabdomyoblastic differentiation in a diagnosed case of MPNST.

MTT is aggressive, with a poorer prognosis than classical MPNST.[4] The 5-year survival rate of MTT is 3%–10% when compared with 50%–60% for classical MPNST.[6] Thus, MTTs must be differentiated from MPNSTs for prompt and aggressive treatment. Resection of the tumor with wide margins followed by radiotherapy is the recommended treatment.[4],[6]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

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1Weiss SW, Goldblum JR. Malignant tumors of peripheral nerves. In: Weiss SW, Goldblum JR, editors. Enzinger and Weiss's Soft Tissue Tumors. 5th ed. China: Mosby Elsevier; 2008. p. 903-44.
2Masson P. Recklinghausen's neurofibromatosis, sensory neuromas and motor neuromas. In: Libman Anniversary. Vol. 2. New York, NY: International Press; 1932. p. 793-802.
3Woodruff JM, Chernik NL, Smith MC, Millett WB, Foote FW. Peripheral nerve tumors with rhabdomyosarcomatous differentiation (malignant ''triton'' tumors). Cancer 1973;32:426-39.
4Stasik CJ, Tawfik O. Malignant peripheral nerve sheath tumor with rhabdomyosarcomatous differentiation (malignant triton tumor). Arch Pathol Lab Med 2006;130:1878-81.
5Kasahara M, Yamagishi Y, Yagi Y. Cytological and histological findings: “Triton tumor” or malignant neurilemmoma complicated with rhabdomyosarcoma. J Jpn Clin Cytol 1983;22:871-80.
6Sundaram S, Prathiba D, Rajendiran S, Rao S, Ganesh K. Squash preparation of a malignant triton tumor in a rare location. J Cytol 2008;25:28-32.