Cytogenetic study of malignant triton tumor: a case report

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Abstract

Malignant triton tumor (MTT) is a highly malignant neoplasm, classified as a variant of malignant peripheral nerve sheath tumor (MPNST) with rhabdomyoblastic differentiation. Few cytogenetic studies of MTT have been reported using conventional cytogenetic analysis. Here, we report a comprehensive cytogenetic study of a case of MTT using G-banding, Spectral Karyotyping, and fluorescence in situ hybridization (FISH) for specific regions. A complex hyperdiploid karyotype with multiple unbalanced translocations was observed: 48∼55,XY,der(7)add(7)(p?)dup(7)[2],der(7) t(7;20)(p22;?)ins(20;19)[5],der(7)ins(8;7)(?;p22q36)t(3;8)t(8;20)[15],−8[5],−8[19],r(8)dup(8), +der(8)r(8;22)[4],−9[9],der(11)t(11;20)(p15;?)ins(20;19)[22],der(12)t(8;12)(q21;p13)[21],der(13) t(3;13)(q25;p11),−17,−19,der(19)t(17;19)(q11.2;q13.1),−20,−22,+4∼7r[cp24]/46,XY[13]. The 1995 International System for Human Cytogenetic Nomenclature was followed where possible. Note that breakpoints were frequently omitted where only SKY information was known for a small part of an involved chromosome. Our analysis revealed some breakpoints in common with those previously reported in MTT, MPNST, and rhabdomyosarcoma, namely 7p22, 7q36, 11p15, 12p13, 13p11.2, 17q11.2, and 19q13.1. FISH showed high increase of copy number for MYC and loss of a single copy for TP53.

Introduction

Malignant peripheral nerve sheath tumors (MPNST) constitute 5%–10% of malignant soft tissue tumors. Karyotypes of these tumors are often complex, with both numerical and structural changes described for all chromosomes [1]. MPNST with muscle differentiation is also known as malignant triton tumor (MTT) [2]. Relatively mature rhabdomyoblasts are scattered throughout a stroma resembling classic MPNST [3]. This rare variant of MPNST is often seen in patients with neurofibromatosis 1 (NF1) and typically involves the head, neck and trunk [4]. Few chromosome analyses of MTT exist. We report here comprehensive cytogenetic analyses of a case of MTT occurring in an individual without recognized NF1.

Section snippets

Case history

An 81-year-old male who was known to have Paget disease of the bone was incidentally found to have a 15-cm retroperitoneal mass. At laparotomy a large left abdominal mass was present with solid and cystic components. Small and large bowel was adherent to the mass, and several peritoneal implants were observed. Pathology showed a metastatic malignant triton tumor. Histologically, the tumor was biphasic with areas of MPNST showing tactoid differentiation and rhabdomyosarcoma. Immunohistochemistry

Cytogenetic analysis

Short-term culture was performed on the metastatic tissue using standard methods to obtain metaphases. The tumor specimen was mechanically and enzymatically disaggregated using collagenase (Worthington type II, 400 μg/mL) for 2–4 hours. The resulting cell suspension was cultivated in RPMI-1640 medium (BioWhittaker, Walkersville, MD, USA) supplemented with 20% fetal bovine serum, penicillin 100 U/mL, streptomycin 100 μg/mL, and 2 mmol/L l-glutamine (Gibco, Grand Island, NY, USA) in an atmosphere

Results

Thirty-seven metaphases (20 G-banded and 17 SKY) were analyzed. Thirteen metaphases had an apparently normal karyotype, whereas the remaining 24 had structural and numerical abnormalities. In spite of the biphasic morphology of the tumor, the cytogenetic analyses revealed a composite karyotype with consistent markers. Some markers were relatively constant while others were highly variable. Clonal loss of chromosomes 8, 17, 19, 20, and 22 was observed, though SKY revealed portions of some of

Discussion

The cell of origin of MTT is not known, though the presence of both neural cells and rhabdomyoblasts have led some to hypothesize that both cellular components derive from less differentiated neural crest cells that have both mesodermal and ectodermal potential and thus possess the ability to develop both skeletal and neural components [7]. Direct evidence for the potential of schwannoma cells to exhibit myogenic differentiation has been shown [8].

Cytogenetic analyses of MTT are limited;

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