Supernumerary Ring Chromosomes Derived from the Long Arm of Chromosome 12 as the Primary Cytogenetic Anomaly in a Rare Soft Tissue Chondroma

Supernumerary Ring Chromosomes Derived from the Long Arm of Chromosome 12 as the Primary Cytogenetic Anomaly in a Rare Soft Tissue Chondroma

Supernumerary Ring Chromosomes Derived from the Long Arm of Chromosome 12 as the Primary Cytogenetic Anomaly in a Rare Soft Tissue Chondroma Farhad F...

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Supernumerary Ring Chromosomes Derived from the Long Arm of Chromosome 12 as the Primary Cytogenetic Anomaly in a Rare Soft Tissue Chondroma Farhad F. Shadan, James T. Mascarello, Robert O. Newbury, Tom Dennis, Patricia Spallone, and A. D. Stock

ABSTRACT: Supernumerary ring chromosomes varying with respect to both size and number were found as the primary cytogenetic anomaly in a rare benign soft tissue chondroma resected from the floor of the mouth of a 3-year-old girl. Reverse fluorescence in situ hybridization paint probes prepared by polymerase chain reaction from microdissected rings produced fluorescent signal over two large but discontinuous parts of the chromosome 12 long arm, subdivided into four regions. This case expands the spectrum of mesenchymal neoplasms in which ring chromosomes have been described as the primary genetic anomaly. A review of the literature reporting similar findings in other soft tissue tumors further supports the possibility that low-level amplification of chromosome 12 long-arm regions may contribute to abnormal cellular proliferation in a variety of mesenchymal tumors. Genes implicated in the control of the cell cycle such as sarcoma amplified sequence (SAS), the human homolog of the murine double-minute type 2 gene (MDM-2), proto-oncogenes CHOP/GADD153, GLI, A2MR, cyclindependent kinase (CDK4), and the high mobility group (HMGIC) gene implicated in mesenchymal tumorigenesis are all located on the long arm of chromosome 12. Chromosomal abnormalities involving the 12q13–q15 region are associated with a wide range of benign soft tissue tumors and sarcomas. © Elsevier Science Inc., 2000. All rights reserved.

INTRODUCTION Although uncommon in most other neoplasms, ring chromosomes are a relatively frequent finding in tumors having mesenchymal origin and borderline malignancy [1]. Chromosome rings have been described in dermatofibrosarcoma protuberans, parosteal osteosarcomas, chondroblastoma, malignant fibrous histiocytoma, atypical lipomatous tumor (well-differentiated liposarcoma, lipoma, or lipoma-like), but not in benign soft tissue chondromas [2–9]. Also common in mesenchymal tumors are anomalies involving the long arm of chromosome 12. Such anomalies have been found in both malignant and benign neoplasms including malignant myxoid liposarcoma, clear cell sarcoma, chond-

From the Department of Internal Medicine, Scripps Clinic (F. F. S.), La Jolla, California, USA; Children’s Hospital—San Diego (J. T. M., R. O. N.), San Diego, California, USA; and the Molecular Cytogenetics/Chromosome Microdissection Laboratory, Nevada Genetics Network, LabCorp (T. D., P. S., A. D. S.), Reno, Nevada, USA. Address reprint requests to: Farhad F. Shadan, Scripps Clinic, Internal Medicine, 10666 N. Torrey Pines Road, La Jolla CA 92037. Received June 16, 1999; accepted September 8, 1999. Cancer Genet Cytogenet 118:144–147 (2000)  Elsevier Science Inc., 2000. All rights reserved. 655 Avenue of the Americas, New York, NY 10010

rosarcoma, leiomyoma, myoma, lipoma, atypical lipomatous tumors, pulmonary hamartoma, hemagiopericytoma, and chondroma [1–10]. We describe here supernumerary ring chromosomes derived from the chromosome 12 long arm as the primary cytogenetic anomaly of a rare soft tissue chondroma. CLINICAL CASE REPORT The patient was a 3-year-old girl with a 2-month history of a progressively enlarging painless sublingual mass. A firm noncystic mass was confirmed by magnetic resonance imaging (MRI) with gadolinium to be at midline within the sublingual space. The enhancing mass did not appear to extend below the level of the mylohyoid muscles; it measured approximately 2.7 cm in maximum dimension and was not associated with adenopathy. The excised mass had a firm consistency and a glistening, greyish white cartilaginous surface. Histologically, the tumor was composed of lobules and sheets of mature cartilage with small foci of ossification (Fig. 1). Small numbers of binucleated chondrocytes were observed. There was no evidence of cytologic atypia or malignancy. Similarly, lipomatous areas, atypical spindle cells and atypical mutlinucleated gi-

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Supernumerary Ring Chromosomes in Chondroma ant cells with spindle cells (characteristic of lipoma, dermatofibrosarcoma protuberans, and malignant fibrous histiocytoma, respectively) were not seen. Tissue samples were examined independently by four pathologists, all of whom concurred with the diagnosis of a rare benign soft tissue chondroma. MATERIALS AND METHODS Cytogenetic study was performed on in situ cultures initiated from a tumor biopsy disaggregated with collagenase (450 units/mL, type IV). Cultures were harvested with standard in situ methods 3 days after initiation, and 22 G-banded metaphase cells were analyzed. Microdissection and reverse fluorescence in situ hybridization (FISH) paint probe preparation were carried out according to previously published methods [11]. Four cells were analyzed and photographed after sequential G-banding followed by fluorescence in situ hybridization. RESULTS In the cytogenetic study of the G-banded metaphase cells analyzed, every metaphase contained from two to five ring

Figure 1 Histological appearance of chrondroma arising in the floor of the mouth of a 3-year-old child: (A) low magnification view; (B) high magnification view.

Figure 2 Partial karyotypes of rings and chromosome 12 pairs from three cells illustrating variation in size and number of rings.

chromosomes with sizes ranging from that of a B-group chromosome down to that of a D-group chromosome (Fig. 2). By itself, the banding pattern of the rings did not suggest a chromosome of origin. Whereas the only anomaly in most cells was the supernumerary rings, three cells contained an extra chromosome 17 in addition to the rings. To identify the origin of the rings, reverse-FISH paint probe was prepared from the microdissected ring chromosomes and hybridized to normal metaphase cells that had been previously G-banded and photographed. A comparison of the G-banded image with the FISH image revealed that there were two main regions of hybridization and that both were located on the long arm of chromosome 12 (Fig. 3). We interpreted the first region as extending from band q13 through band q21 and the second as extending from band q23 through band q24.1, with subdivisions including q13.3, q14.2, q24.11, and q24.13, respectively. On the basis of ISCN nomenclature, the tumor karyotype was described as: 48ⵒ51,XX,⫹2ⵒ5r(12).rev ish(12)(q14q24.1) [18]/49ⵒ50,XX,⫹2ⵒ3r(12),⫹17.rev ish(12)(q14q24.1)[4].

DISCUSSION The histological assessment of the tumor described here was entirely consistent with that expected for a rare benign soft tissue chondroma. Soft tissue chondromas of the floor of the mouth are extremely uncommon tumors and are particularly so in children. In adults, they usually arise in the extremities but, in children (as in our case), their location can be more variable [12]. Histologically, they may be confused with low-grade chondrosarcoma [13]. However, chondrosarcomas are rare in childhood and usually exhibit greater cellularity, pleomorphism, and nuclear atypia than was seen in our case. If ossified, chon-

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Figure 3 Partial cell photographs of normal cell after G-banding (A) and the same cell after FISH (B) with a paint probe prepared from microdissected chondroma ring chromosomes. Paint probe produces fluorescent signal over two major regions on the chromosome 12 long arm.

dromas can resemble myositis ossificans, but our case exhibited very little ossification. Furthermore, none of the histological features considered diagnostic of the other ring chromosome-associated mesenchymal tumors were present in this case. In our case, supernumerary rings derived from the chromosome 12 long arm were the primary cytogenetic anomaly. As far as we are aware, rings have not been previously reported in chondromas, but other anomalies involving the chromosome 12 long arm have been noted [14, 15]. Supernumerary rings and other anomalies that result in low-level amplification of chromosome 12 long-arm sequences have been reported in a number of other soft tissue tumors including atypical lipomatous tumors, (well-differentiated liposarcoma, lipomas, and lipoma-like) malignant fibrous histiocytoma, chondroblastma, dermatofibrosarcoma protouberans, parosteal osteosarcoma, pleomorphic liposarcoma, glioma, neuroblastoma, and Ewing sarcoma [1–7, 9, 16, 17]. This report, therefore, expands the spectrum of mesenchymal neoplasms in which ring chromosomes have been described. Our review of the literature suggests that the presence of multiple ring chromosomes as the primary cytogenetic anomaly may play a role in the support of gene amplification associated with the development of mesenchymal tumors in general. Genes implicated in the control of the cell cycle such as sarcoma amplified sequence (SAS), the human homolog of the murine double-minute type 2 gene (MDM-2), proto-oncogenes CHOP/GADD153, GLI, A2MR, cyclin-dependent kinase (CDK4), and the high mobility group (HMGIC) gene implicated in mesenchymal tumorigenesis [18–21] are all located on the long arm of chromosome 12 [22–25]. Chromosomal abnormalities involving

the 12q13ⵒq15 region are associated with a wide range of benign soft tissue tumors and sarcomas [2, 22, 26–32]. The discontinuous pattern of chromosome 12 fluorescence produced by our microdissection paint probe is remarkably similar to the pattern of chromosome 12 amplification found in comparative genomic hybridization and FISH studies of benign and atypical lipomatous tumors [3, 9]. There is, therefore, significant evidence reported in the literature that supports the potential role of such amplicons in the development of mesenchymal tumors in general. We thank Drs. H. Krous, G. Billman, L. Dehner, D. Kearns, L. Harvey, and P. Haghighi for their contributions to the case.

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